187
Ministry of Higher Education & Scientific Research University of Baghdad College of Engineering Mechanical Engineering Department Incompressible Fluid Mechanics Prof. Dr. Ihsan Y. Hussain Mech. Engr. Dept. / College of Engr. University of Baghdad February 2017 Jamada Al-Aoula 1438

Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

  • Upload
    others

  • View
    4

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Ministry of Higher Education & Scientific Research

University of Baghdad – College of Engineering

Mechanical Engineering Department

Incompressible Fluid Mechanics

Prof. Dr. Ihsan Y. Hussain

Mech. Engr. Dept. / College of Engr. – University of Baghdad

February 2017 Jamada Al-Aoula 1438

Page 2: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 2

Preface

The present book is a handout lectures for the B.Sc. Course

ME202 : Fluid Mechanics / I. The course is designed for B.Sc. Sophomore Students in

the Mechanical Engineering Discipline. The time schedule needed to cover the course

material is 32 weeks, 3 hrs. per week. The course had been taught by the author (course

tutor) for more than 25 years. A short c.v. for the author is given below;

Prof. Dr. Ihsan Y. Hussain / Baghdad - 1964

B.Sc. ( 1986 ), M.Sc. ( 1989 ), & Ph.D. ( 1997 ) in Mechanical

Engineering from the Mech. Engr. Dept. – University of Baghdad

Professor of Mechanical Engineering – Thermo-Fluids

Teaching Undergraduate Courses and Laboratories in Various

Iraqi Universities ( Baghdad, Al-Kufa, Babylon, Al - Nahrain ….)

in Various Subjects of Mechanical Engineering

Teaching Advanced Graduate Courses (M.Sc. and Ph.D.) in various

Iraqi Universities (Baghdad, Technology, Babylon, Al-Kufa, Al-Mustansyrya, Al-

Nahrain…) in the Areas of ( Fluid Mechanics, Heat Transfer, CFD, Porous Media, Gas

Dynamics, Viscous Flow, FEM, BEM

Lines of Research Covers the Following Fields ;

Aerodynamics

Convection Heat Transfer ( Forced, Free, and Mixed )

Porous Media ( Flow and Heat Transfer )

Electronic Equipment Cooling

Heat Transfer in Manufacturing Processes ( Welding, Rolling, … etc. )

Inverse Conduction

Turbomachinery ( Pumps, Turbines, and Compressors )

Heat Exchangers

Jet Engines

Phase-Change Heat Transfer

Boundary Layers ( Hydrodynamic and Thermal )

Head of the Mech. Engr. Dept. / College of Engineering - University of Baghdad ( December

/ 2007 – October / 2011 )

Member of Iraqi Engineering Union (Official No. 45836).

ASHRAE Member ( 8161964 )

Head of ( Quality Improvement Council of Engineering Education in Iraq QICEEI )

Supervised ( 41 ) M.Sc. Thesis and ( 20 ) Ph.D. Dissertations

Publication of more than (70) Papers in the Various Fields Mentioned above

Member in the Evaluation and Examining Committees of more than ( 300 ) M.Sc. and Ph.D.

Students in their Theses and Dissertations

Member of the Editing Committee of a number of Scientific Journals

Evaluation of more than ( 700 ) Papers for Various Journals and Conferences

Working within the Mechanical Groups in the Consulting Engineering Bureau, College of

Engineering, University of Baghdad, and in the Dept. of Mech. Engr. , in the Mechanical

Design of Various Projects

Contact Information :

E-mail: [email protected] : [email protected] [email protected]

Skype Name : drihsan11

Mobile No. : +964-7901781035 : +964-7705236582

Page 3: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 3

"Table of Contents"

Section Page

No.

Table of Contents 3

I. Preface 7

I.1 General Approach 7

I.2 Learning Tools 7

I.3 Contents 9

I.4 Time Scheduling Table 10

I.5 Laboratory Experiments 10

I.6 Textbook and References 11

I.7 Assessments 11

Chapter -1- : Introductory Concepts 12

1.1 Definition of Fluids and Fluid Mechanics 12

1.2 Scope and Applications of Fluid Mechanics 14

1.3 Dimensions and Units 15

1.4 Newton's Law of Viscosity for Fluids 16

1.5 Basic Definitions and Concepts 18

Examples 25

Problems 27

Chapter - 2- : Fluid Statics 28

2.1Introduction 28

2.2 Pressure Variation in a Static Fluid 28

2.2.1 Pressure Variation with Direction 28

2.2.2 Pressure Variation in Space 29

2.2.3 Basic Hydrostatic Equation 30

2.2.4 Pressure Variation for Incompressible Fluids 31

2.2.5 Pressure Variation for Compressible Fluids 31

2.3 Pressure Measurements 32

2.3.1 Absolute and Gage Pressure 32

2.3.2 Atmospheric Pressure Measurements 33

2.3.3 Gage Pressure Measurements 34

2.3.3.1 Bourdon Gage 34

2.3.3.2 Pressure Transducers 34

2.3.3.3 Manometers 34

2.3.3.3.1 Piezometer 35

2.3.3.3.2 Differential Manometers 36

2.3.3.3.3 Micro Manometer 36

2.3.3.3.4 Inclined Manometer 36

2.4 Hydrostatic Forces on Submerged Surfaces 37

2.4.1 Horizontal Surfaces 37

2.4.2 Inclined Surfaces 38

Page 4: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 4

2.4.3 Curved Surfaces 40

2.5 Buoyancy 42

2.5.1 Hydrometers 44

2.6 Stability of Submerged and Floating Bodies 44

2.6.1 Submerged Bodies 44

2.6.2 Floating Bodies 45

2.6.3 Metacenter 46

2.7 Relative Equilibrium 47

2.7.1 Uniform Linear Acceleration 47

2.7.2 Uniform Rotation 49

Examples 50

Problems 55

Chapter -3- : Fluid Flow Concepts 56

3.1 Definitions and Concepts 56

3.2 General Control Volume Equation 61

3.3 Law of Conservation of Mass: Continuity Equation 63

3.3.1 Continuity Equation at a Point 63

3.4 Law of Conservation of Energy: Energy Equation 64

3.4.1 Bernoulli's Equation 67

3.5 Law of Conservation of Liner Momentum: Momentum Equation 69

3.5.1 Applications of Momentum Equation 70

3.5.1.1 Fixed Vanes (Blades) 70

3.5.1.2 Moving Vanes (Blades) 71

3.5.1.2.1 Single Moving Vane 71

3.5.1.2.2 Series of Moving Vanes 72

3.5.1.3 Forces on pipe Bends 73

3.5.1.4 Theory of Propellers 74

3.5.1.5 Jet Propulsion 75

3.5.1.6 Rocket Mechanics 76

3.5.2 Euler's Equation of Motion 77

3.5.3 Bernoulli's Equation 77

3.6 Some Applications of Continuity, Momentum and Energy Equations 78

3.6.1 Losses due to Sudden Expansion 78

3.6.2 Hydraulic Jump 79

3.7Law of Conservation of Angular Momentum: Moment of Momentum

Equation

79

Examples 81

Problems 87

Chapter -4- : Dimensional Analysis And Similitude 88

4.1 Introduction 88

4.1.1 Dimensions and Units 88

4.2 Dimensional Analysis 90

4.2.1 The Buckingham II - Theorem 91

Page 5: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 5

4.2.2 Common Dimensionless Numbers 93

4.3 Similitude 96

4.3.1 Re - Criterion 98

4.3.2 Fr - Criterion 98

4.4 Ships Models Tests 99

Examples 101

Problems 103

Chapter -5- : Viscous Fluid Flow 104

5.1 Introduction 104

5.2 Equations of Motion for Viscous Flow 104

5.3 Laminar Flow Between Parallel Plates: Couette Flow 106

5.4 Losses in Laminar Flow 108

5.5 Laminar Flow Through Circular Tubes and Annuli 110

5.5.1 Circular Tubes : Hagen - Poiseuille Equation 111

5.5.2 Annuli 112

5.6 Boundary - Layer Flow 113

5.6.1 Laminar Boundary - Layer 114

5.6.2 Turbulent Boundary - Layer 115

5.6.3 Boundary - Layer Separation 116

5.7 Drag an Lift 118

5.8 Resistance to Flow in Open and Closed Conduits 119

5.8.1 Open Channels Flow 121

5.8.2 Steady Incompressible Flow Through Pipes 121

5.8.3 Simple Pip Problems 123

5.8.4 Secondary (Minor) Losses 124

Examples 127

Problems 135

Chapter -6- : Fluid and Flow Measurements 136

6.1 Density Measurements 136

6.2 Pressure Measurements 136

6.2.1 Static Pressure measurements 137

6.2.2 Total (Stagnation) Pressure Measurements 138

6.3 Velocity Measurements 138

6.4 Discharge Measurements 140

6.4.1 Orifice Meters 140

6.4.1.1 Orifice in Reservoirs 140

6.4.1.2 Orifice in Pipes 143

6.4.2 Venturi Meter 144

6.4.3 Rotameter 145

6.5 Viscosity Measurements 145

6.5.1 Rotating Concentric Cylinders 145

6.5.2 Capillary Flow method 146

6.5.3 Say bolt Viscometer 146

Page 6: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 6

Examples 148

Problems 150

Chapter -7- : Closed Conduits Flow Networks 151

7.1 Introduction 151

7.2 Pipe Friction Formula 151

7.3 Concept of Hydraulic and Energy Grade Lines 152

7.4 Combination of Pipes 154

7.4.1 Pipes in Series 154

7.4.2 Pipes in Parallel 155

7.4.3 Branching Pipes 156

7.4.4 Pipe Networks 157

7.5 Pumping Stations 158

7.5.1 Single Pump in Pipe Line 158

7.5.2 Pumps in Series 160

7.5.3 Pumps in Parallel 161

7.6 Conduits with non - Circular Cross - Section 162

Examples 163

Problems 171

Appendix –A- : Course Folio 172

Page 7: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 7

I. Preface

I.1 General Approach

The present “Lecture Notes" are intended for use in a first course in “Fluid

Mechanics" for under - graduate engineering student in the sophomore years. It represents

the revision of lecture notes for about 25- years experience in teaching the subject of

(Fluid Mechanics / I) in the second year at the Mechanical Engineering Department /

College of Engineering - University of Baghdad and other Iraqi universities. The text

covers the basic principles of fluid mechanics with a broad range of engineering

applications.

The students are assumed to have completed the subject of (Engineering Mechanics

/ Statics & Dynamics) and (Mathematics / I) courses. The relevant concepts from theses

two subjects are introduced and reviewed as needed. The emphasis throughout the text is

kept on the "physics" and the “physical arguments" in order to develop an “intuitive

understanding" of the subject matter.

Throughout the text, we tried to match between engineering education and

engineering practice. The text covers all the standard topics in fluid mechanics with an

emphasis on physical mechanisms and practical applications, while de – emphasizing

heavy mathematical aspects, which are being left to computers. We try to encourage

“Creative Thinking" and development of a “Deeper Understanding" of the subject matter

by the students.

I.2 Learning Tools

The emphasis in the text is on "developing a sense of underlying physical

mechanism" and a “mastery of solving practical problems" an engineer is likely to face in

the real world. Thus, the text covers more material on the fundamentals and applications

of fluid mechanics. This makes fluid mechanics a more pleasant and worthwhile

experience for the student.

The principles of fluid mechanics are based on our “everyday experiences" and "

experimental observations". A more physical intuitive approach is used through the text.

Page 8: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 8

Frequently, “Parallels are drawn" between the subject matter and students' every day

experiences so that they can relate the subject matter to what they already know.

The material in the text is introduced at a level that an average student can follow

comfortably. It speaks "to" the students, not "over" the students. All- derivations in the

text are based on physical arguments with simple mathematics, and thus they are easy to

follow and understand.

Figures are important learning tools that help the students “get the picture". The text

makes effective use of graphics.

A number of worked –out examples are included in the chapters of the text. These

examples clarify the material and illustrate the use of basic principles. An intuitive and

systematic approach is used in the solution of the example problems.

A number of sheets of solved problems that covers the material of the subject are also

included in the appendices. These problems are focusing on the application of concepts

and principles covered in the text in solving engineering problems related to important

application of the subject.

At the end of each chapter, a number of selected unsolved problems from related

chapters in the “textbook" used during the course (reference (1)) in the list of references)

are listed. The problems are grouped under specific topics (articles) in the order they are

covered to make problem selection easier for the student.

A collection of examination paper is also included in the appendices. The collection

covers quizzes, mid-term exams, comprehensive exam and final exams. It serves as a tool

to improve students’ way of thinking and to make them familiar with the nature of

examinations questions.

A number of quizzes are usually made during the teaching period of the subject (about

32 weeks). These many quizzes serve the following;

1. Make these students familiar with the environment of the examinations.

2. Continuous study and follow-up from students to the material of the subject.

3. A “bank" of miscellaneous questions covering the various applications of the subject

material will be available for both students and instructor.

Page 9: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 9

4. The final average mark will be distributed on large number of quizzes and tests, so

that, the shortage in one or more of these quizzes will not affect the evaluation greatly.

A number of laboratory experiments (7-10) are made to cover the principle and

concepts of the subject, experimentally. These experiments help to give the student skills

of dealing with the devices set up, acquiring and recording data, writing reports, analysis

and discussion of the results, conclusions and recommendations.

I.3 Contents

The lecture note comprises seven chapters and a number of appendices. The first five

chapters cover the basic fundamentals of the material, while the last two ones involve the

important applications of the subject.

In chapter -1- we introduce the basic fundamental concepts and definitions of fluid

mechanics as a science and its applications in the real world. Chapter -2- presents the

basic concepts of fluid statics and its application in engineering and industry. It includes

the derivation of hydrostatic pressure variation, pressure measurements, forces on

submerged surfaces, buoyancy and stability of immersed and floating bodies and relative

equilibrium. In chapter-3-, the fundamentals of fluid motion are studied. The governing

continuity, energy and momentum equations are derived by using the Reynolds-transport

theorem. The various applications of these equations are introduced. Chapter-4- covers the

dimensional analysis and similitude principles and their applications. In chapter-5-, the

real (viscous) fluid flow is considered. Various applications of this type of fluid flow are

investigated, which include: laminar flow between parallel plates and through circular

tubes and annuli, boundary-layer flow, drag and lift, Moody diagram and simple pipe

problems. Chapter-6- concerns the measurements of fluid and flow properties. These

include density, pressure, velocity, flow rate and viscosity measurements. In chapter -7-,

the analysis of pipes and pumps connection is introduced. Series, parallel and branching

pipes networks are analyzed. Besides, series and parallel pumps connection in pumping

stations is considered. The appendices include solved sheets of problems, collection of

examination papers sheets of problems, collections, collection of examination papers and

test questions.

Page 10: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 10

I-4 Time Scheduling Table

The subject teaching period is (32 weeks), (4 hrs.) per week (3hrs. theory and 1 hr.

tutorial). The following is the time scheduling table for the subject weekly outlines, see

Table (I.1). This time schedule is for the theoretical part of the subject only.

Table (I.1): Time Scheduling Table

Week Covered Articles Tests Week Covered Articles Week

1

Ch

ap

ter

-1-

1.1+1.2+

1.3+1.4 17

C

hap

ter

Ch

ap

ter

-5

-

-

4-

4.1+4.2+4.2.1

2 1.5 Q1 18 4.2.2+4.3+4.3.1 Q11

3

Ch

ap

ter

-2-

2.1+2.2 Q2 19 4.3.2+4.4 Q12

4 2.3 20 5.1+5.2+5.3 Q13

5 2.4.1+2.4.2 Q3 21 5.4+5.5 Q14

6 2.4.3 22 5.6+5.6.1+5.6.2 Q15

7 2.5 Q4 23 5.6.3+5.7 Q16

8 2.6.1+2.6.2 Q5 24 5.8+5.8.1 Q17

9 2.6.3 25 5.8.2 Q18

10 2.7.1 Q6 26 5.8.3+5.8.4 Q19

11 2.7.2 27

Ch

ap

ter

-6-

6.1+6.2+6.3 Q20

12

Ch

ap

ter

-3-

3.1+3.2+3.3 Q7 28 6.4 Q21

13 3.4 29 6.5 Q22

14 3.5+3.5.1.1

to 3.5.1.3 Q8 30

Ch

ap

ter

-7-

7.1+7.2+7.3 Q23

15

3.5.1.4 to

3.5.1.6+

3.5.2+3.5.3

Q9 31 7.4 Q24

16 3.6+3.7

Q10

+

TEST

I

32 7.5+7.6

Q25

+

Test

II

Note: The experimental part of the subject (1 hr. per week) in addition to

the 4 hrs. (3 theory + 1 tutorial), see the following article.

I.5 Laboratory Experiments

We should mention here that the experimental part of the subject (1 hr per week) is

included in a separate general “Mechanical Engineering Laboratories/II" course. It

involves a number of experiments covering the principles and concepts of the subject

material. As was mentioned earlier, the experimental part aims to acquire the student a

skill of dealing with the devices, recording test data, writing a report, analysis and

Page 11: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 11

discussion of the results, presentation of the experimental observations and results, and

conclusions and recommendations drawn from the results. The following is a list of some

of these experiments;

1. Dynamic Similarity.

2. Meta centric Height.

3. Impact of Jet.

4. Friction in Pipes.

5. Minor Losses.

6. Flow Measurements (Orifice and Venturi Meters).

7. Stability of Floating Bodies.

8. Bernoulli’s Equation Demonstration.

I.6 Textbook and References

The text adopted in teaching the subject is;

"Fluid Mechanics", by victor L.Streeter and E. Benjamin Wylie; First SI metric Edition,

Mc.Graw Hill, 1988

Other references which may be used are listed below;

1. "Elementary Fluid Mechanics", by John k.Vennard and Robert L. Street, 5th

edition, John Wylie and Sons,1976

2. "Engineering Fluid Mechanics", by John A. Roberson and Clayton T. Crow, 2nd

Edition, Houghton Mifflin Co.,1998

I.7 Assessments

The final mark (100%) is distributed along the teaching period as follows;

Activity Mark

Quizzes (15-20 Nos.) 15%

Comprehensive Tests (2Nos.) 10%

Extracurricular Activities 5%

Final Test 70%

Total Sum 100%

The Passed Average Required is (50%)

Page 12: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 12

Chapter -1-

Introductory Concepts

1.1 Definition of Fluids and Fluid Mechanics

According to the variation of volume and shape with pressure, the state of matter is

usually classified in to three states, solid, liquid and gas, see Fig. (1). Fluids in clued the

liquids and gases.

Fluids

Fig. (1)

Fluid

It is a substance that deforms continuously when subjected to shear stress, no

matter how small that shear stress may be. Fluids may be either liquids or gases. Solids,

as compared to fluids, cannot be deformed permanently (plastic deformation) unless a

certain value of shear stress (called the yield stress) is exerted on it.

According to the variation of density of the fluids with pressure, fluids are

classified in to "incompressible" and "compressible" fluids.

Solid

Fixed Volume

Fixed Shape

Molecular Spacing ≃ 1 °A

(1 °A =10-10

m)

Liquid

Fixed Volume

Variable Shape

Molecular Spacing ≃ 102–103 °A

Gas

Variable Volume

Variable Shape

Molecular Spacing ≃ 104 °A

Page 13: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 13

Incompressible Fluids

They are the fluids with constant density, or the change of density with pressure is

so small that can be neglected and considers the density as constant. The incompressible

fluids are basically the "LIQUIDS". Gases at low velocities are usually considered as

incompressible fluids also.

There are no exact incompressible fluids in practice. For example, the density of

water at atmospheric pressure (0.1 MPa) is (1000 kg/m3). When the pressure is increased

to (20 MPa), the density becomes (1010 kg/m3). Thus, increasing the pressure by a factor

of (200) increases the density by only (1%)!! For this reason, it is reasonable to consider

the liquids as incompressible fluids with constant density.

Compressible Fluids:

They are the fluids with variable density, or the change of density with pressure is

large and cannot be neglected. These include basically the "GASES". In some liquids

problems, such as "water hammer", the compressibility of liquids must be considered.

Fluid Mechanics

It is the science that deals with the action of forces on fluids, which may be either

liquids or gases. Fluid mechanics, as a science, is a branch of the "Engineering

Mechanics" as a general science deals with the action of forces on bodies or matter

(solids, fluids (liquids of gases)), see Fig. (2).

Fig. (2)

Engineering Mechanics

Mechanics of Rigid

Bodies

Solids

Kinematics Kinetics

Mechanics of Deformable

Bodies

(Strength of Material)

Mechanics of Fluids

(Liquids & Gases)

Fluids

Page 14: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 14

1.2 Scope and Applications of Fluid Mechanics

Fluids and Fluid Mechanics play a vital role in our daily life. Large and diverse

applications which are based on fluid mechanics exist. Typical examples are listed below;

1- Irrigation.

2- Navigation.

3- Power Generation (Hydraulic, Gas and Steam Power Plant).

4- Ships, Boats and Submarines.

5- Airplanes and Hovercrafts:

a. Wing Surfaces to Produce Lift.

b. Jet Engines to Produce Thrust.

c. Fuselage Design for Minimum Drag.

d. Various Systems in the Air Craft (A/c, Fuel, Oil, Pneumatic).

e. Control of the Airplane (Tail, Flaps, Ailerons, …).

6- Cars and Motorcycles.

a. Pneumatic tires.

b. Hydraulic Shock Absorbers.

c. Fuel System (Gasoline + Air).

d. Air Resistance Grates Drag on Car.

e. Lubrication System.

f. Cooling System.

g. Aerodynamic Design of Car Profile for Minimum Drag.

7- Design of Pipe Networks.

8- Transport of Fluids.

9- Air – Conditioning and Refrigeration Systems.

10- Lubrication Systems.

11- Design of Fluid Machinery (Fans, Blowers, Pumps, Compressors, Turbines,

Windmills, ….).

12- Bioengineering (Flow of Blood through Veins and Arteries).

13- Fluid Control Systems.

14- All Living Creatures Need Water (Fluid) for Life (We Made from Water Every

Living Thing).

Page 15: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 15

1.3 Dimensions and Units

"Dimensions" are physical variables that specify the behavior and the nature of a

certain system, whereas the "Units" are used to specify the amount of these dimensions.

Generally, two systems of units exist. These are the International System of units (SI) and

the United States of units (U.S.). The base quantities in the (SI) system are the Mass (M),

length (L) and time (T), therefore it is called the (MLT- system), whereas in the (U.S.)

system, the base quantities are the force (F), Length (L) and time (T), and is called the

FLT- system. The dimensions are expressed by capital letters. Table (1) lists the

dimensions and units of the most important variables in Fluid Mechanics, in both (SI) and

(U.S.) systems, followed by conversion factors between the two systems.

Table (1): Dimensions and Units

Physical

Quantity Dimension

Units

SI U.S.

Mass M kg Slug

Length L m ft

Time T s sec.

Force F N lbf

Temperature o C

K

o F (Ordinary

Temp.) o R (Absolute

Temp.)

Area L2 m

2 ft

2

Velocity LT-1

m/s ft/sec. (fps)

Acceleration LT-2

m/s2 ft/sec

2

Work FL

(ML2T

-2)

N.m (J) lbf . ft

Power FLT

-1

ML2T

-3

N.m /s (

), W lbf.ft / sec.

Pressure FL

-2

ML-1

T-2

N/m

2 (Pa) lbf / ft

2 (psf)

Density ML-3

kg / m3 Slug / ft

3

Conversion Factors

1- Slug = 14.59 kg

Slug= 32.2 lbm

1 lbm = 0.4536 kg

Page 16: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 16

2- 1 ft = 0.3048 m

1 ft = 12 in

1 in = 2.54 cm

1 mile = 5280 ft

1 mile = 1609 m.

3- 1 lbf = 4.448 N

1 N = (1 kg) (1 m/s2)

1 lbf = (1 Slug) (1 ft/sec2)

4- K= oC + 273

oR=

oF + 460

oF = 1.8

oC + 32

oR=1.8 K

Prefixes

G = 109 gega m = 10

-3 milli

M = 106 mega = 10

-6 micro

k = 103 kilo n = 10

-9 nano

c = 10-2

centi p = 10-12

pico

1.4 Newton's Law of Viscosity for Fluids

Consider a fluid placed between two closely spaced parallel plates so large that

conditions at their edges may be neglected. The lower plate is fixed and a force (F) is

applied at the upper plate which exerts a shear stress (F/A) on any fluid between the

plates, see Fig. (3). The force (F) causes the upper plate to move with a steady velocity

(U), no matter how small the magnitude of (F)

Fig. (3)

The fluid in the immediate contact with a solid boundary has the same velocity as the

boundary; i.e., there is no slip at the boundary. The fluid in the area (abcd) flows to the

Page 17: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 17

new position (ab'c'd), each fluid particle moving parallel to the plate at the velocity (u)

varies uniformly from zero at the stationary plate to (U) at the upper plate. Experiments

show that, other quantities being held constant, (F) id directly proportional to (A) and (U)

and is inversely proportional to thickness (h). In equation form;

Thus;

…………………...... (1.1)

Where; = Proportionality constant, viscosity of the fluid

A = Surface area parallel to the force F

Defining the shear stress ( = F/A), then;

...... (1.2)

The ratio (U/h) is the angular velocity of line (ab), or it is the rate of angular deformation

of the fluid, i.e., the rate at which the angle (bad) decreases. The angular velocity may be

written as (du/dy) as;

(

)

(du / dy) is more general and may be visualized as the rate at which one layer moves

relative to an adjacent layer. Thus, equ. (1.2) may be written as;

(Newton's Law of Viscosity) .................. (1.3)

Materials other than fluids, such as solids and plastics, cannot satisfy the definition of

fluid and equ. (1.3), since they do not deform continuously unless their "yield shear

stress" is applied.

Fluids may be classified as "Newtonian" or ” Non - Newtonian". In Newtonian

fluid, there is a linear relation between the applied shear stress ( ) and the resulting

angular deformation (du/dy) (i.e., is constant in equ. (1.3), see Fig. (4). In Non -

Newtonian fluids, the relation is non - liner. An “ideal plastic" has a definite yield stress

Page 18: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 18

and a constant linear relation of ( ) to (du/dy). A “thixotropic" substance, such as

printer's ink, has a viscosity that is dependent upon the immediate prior angular

deformation of the substance and has a tendency to take a set when at rest. Gases and thin

liquids tend to be Newtonian fluids, while thick, long - chained hydrocarbons may be non

- Newtonian fluids.

Yield Stress

Thixotropic

substance

Fig. (4): Rheological Diagram

1.5 Basic Definitions and Concepts

1- Density( )( )

It is the mass (m) of a fluid per unit volume ( );

…………....... (1.4)

For water at standard pressure (760 mmHg) and 4 °C :

For air at standard pressure (760 mmHg) and 20 °C :

2- Specific Volume ( )

It is the volume occupied by unit mass of fluid; i.e., it is the reciprocal of the

density ( );

……………...... (1.5)

3- Specific Weight (γ) (gama)

It is the force of gravity (weight) (W) of a fluid per unit volume ( ). It is also

called the unit gravity force.

γ

γ = g

,

………….......(1.6)

𝜇 𝜇0 (𝑑𝑢

𝑑𝑦)

(𝜇0 𝑛) 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡𝑠

𝜏

𝑑𝑢

𝑑𝑦

Page 19: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 19

(γ) Changes with location depending upon gravity (g).

γ water =9806 N/m3 at 5 °C at sea level

γ air = 11.8 N/m3 at 20 °C and patmstd = 101325 Pa

4- Specific Gravity (s)

It is the ratio of specific weight of a substance to that of water; it is also the ratio of

the mass of a substance to the mass of an equivalent volume of water at standard

condition. It may also be expressed as a ratio of its density to that of water.

s =

(dimensionless) ……………...... (1.7)

The specific gravity is also called the "relative density”. In equ. (1.7), ( ) is taken as

( N/m3) at standard reference temperature (4 °C). For gases, air or oxygen

are usually taken as the references fluid instead of water.

5- Pressure (p)

It is the normal force (F) pushing against a plane area divided by the area (A), see

Fig. (5);

(

( )

( )) ....

(1.8)

If a fluid exerts a pressure against the walls of a container, the container will exert

a reaction on the fluid which will be compressive. Liquids can sustain very High

compressive pressure, but they are very week in tension. The pressure intensity is a scalar

quantity, has a magnitude only. Pressure may be express in terms of an equivalent height

(h) of fluid column;

p = γ h ……………………… (1.9)

6- Shear Stress ( ) (taw)

It is the shear force (F) acts upon the surface (parallel) area (A), see Fig. (6)

( ) (

) …………...... (1.10)

Fig. (5)

Page 20: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 20

Unlike pressure, shear stress may have two components, see Fig. (6);

…………....... (1.10a) (z xy - plane)

………………..... (1.10b)

7. Viscosity

It is the property of a fluid by virtue of which it offers resistance to shear. There

are two types of viscosity; "Dynamic (or Absolute) viscosity ( ) , and the "Kinematic

Viscosity". Their definitions are;

......................... (1.11) (from Newton's law of viscosity, equ. (1.3))

......................... (1.12)

Units of Viscosity

SI Units:

( )

Poise P =

(

)

U.S. Units:

(

)

Causes of Viscosity:

1. Cohesion forces between molecules, (effective in liquids).

2. Exchange of momentum by molecules in the layers, (effective in gases).

Notes:

1. Viscosity of gases increases with temperature, but viscosity of liquids decreases with

temperature, see Fig. (C.1) and (C.2) p.p (536-537) in your textbook.

Fig. (6)

Page 21: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 21

2. For ordinary pressure, viscosity is independent of pressure.

3. Kinematic viscosity represents the momentum diffusion coefficient; its value for gases

is larger than that for liquids.

8- Specific Heat (c)

It is the property that decries the capacity of a substance to store thermal energy. It

is the amount of heat that must be transmitted to a unit mass of a substance to raise its

temperature by one degree.

For gases, (c) depends on the process accompanied the change in temperature;

accordingly, there are two types;

Specific heat at constant pressure.

Specific heat at constant volume.

Specifics' heat ratio ........………....... (1.13)

R = Gas constant .......................... (1.14)

Examples: Water:

Air:

9- Vapor Pressure ( )

It is the pressure at which a liquid will boil. Vapor pressure is a function of

temperature (it increases with temperature). When the liquid pressure is less than the

Fig. (c.1)

p.p536 in textbook

Fig. (c.2)

p.p.537 in text book

𝜇 𝑣

Page 22: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 22

vapor pressure, liquid flashes into vapor. This is the phenomenon of "cavitation" which

results in the “erosion" of the metal parts.

Ex. Water at (20 °C) has = 2.447 kPa

At (100 °C) has = 101.3 kPa

Mercury at (20 °C) has = 0.173 kPa

10- Equation of State: Perfect Gas

The perfect gas is defined as a substance that satisfies the “perfect gas law"; which has

the following forms;

p =mRT …………………… (1.15a)

p =RT …………………… (1.15 b)

p= RT …………………… (1.15c)

p =nRT …………………… (1.15d)

Where;

R=

…………………………….. (1.15e)

And =

……………………… (1.15f)

p= Absolute Pressure (Pa)

T=Absolute lute Temperature (K)

R= Gas constant (J/kgK)

R=Universal Gas Constant =8312 J/mol K

Mw=Molecular Weight (kg/ mol)

n=Number of Moles

Real gases below critical pressure and above critical temperature tend to obey the

perfect gas law. The perfect law encompasses both Charles' law (which states that for

constant pressure ( ) and Boyle's law (which states that for constant

temperature : )

11- Bulk Modulus of Elasticity (k)

It expresses the compressibility of a fluid (liquids and gasses). It represents the

change of volume (d ) caused by change in pressure (dp). It is defined as;

Page 23: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 23

k =

(Pa) …………………………………… (1.16)

Where:

dp=Change in pressure (Pa)=p2-p1

d =Change in volume (m3) =

d =Charge in density (

) =

=Original volume (m3) =

=Original density (kg/m3) =

For perfect gases;

P= RT

=RT K=

= RT K=p

Ex. Kwater=2.2 Gpa

K air=0.0001 Gpa

12- Surface Tension ( ) (sigma)

At the interface between a liquid and a gas, or two immiscible liquids, a film or

special layer seems to form on the liquid, apparently owing to attraction of liquid

molecules below the surface. It is a simple experiment to place a small needle on a water

surface and observe that it is supported there by the film.

The formation of this film may be visualized on the basis of “surface energy" or

work per unit area required to bring the molecules to the surface. The "surface tension "

is then the stretching force required to form the film, obtained by dividing the surface

energy term by unit length of the film in equilibrium. The surface tension of water varies

from about (0.074

) at (20ºC) to (0.059

) at (100ºC).

Capillarity

Capillarity attraction is caused by surface tension and by the relative value of

“adhesion"(Which is the attraction between liquid particles and solid) to "cohesion"

(which is the molecular attraction between liquid particles), see Fig. (7).

If dp>0 (p2>p1), then:

d < ( < )

d𝜌 > (𝜌 > 𝜌 )

The capillarity rise (h) is usually calculated by applying equilibrium equation to

the capillary tube shown in Fig.(8), and as follows;

Page 24: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 24

cos =w

2 cos =

Thus;

h=

……………. (1.17)

Where;

h = Capillary rise (m)

Wetting angle [for clean tubes,

= ( 0o ) for water and (140º) for mercury]

Note:

1- For d>12 mm, capillary effects are negligible.

2- Equ (1.17) is plotted in Fig. (1.4) in your textbook.

Some Applications of Surface Tension

The action of surface tension is to increase the pressure within droplet, bubble and

liquid jet. To calculate the pressure sustained in these cases, a force balance is made, and

as follows;

1- Droplet

For a section of half of spherical droplet, see Fig. (9);

=

P* =2

Thus:

……………………………. (1.18)

2- Bubble

For a section of half of a spherical bubble, see Fig (10);

= +

p* =2*

Thus;

p=

………………….. (1.19)

Fig. (8)

𝐹𝜎

Fig. (9)

Fig. (10)

𝐹𝜎

𝐹𝜎

𝐹𝑝

Fig. (7)

Page 25: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 25

3- Liquid Jet

For a section of a half of a cylindrical liquid jet, see Fig. (11) ;

= +

p*L2r= =2

Thus p=

…………………. (1.20)

4- Measurements of ( ): Ring Pulled out of a Liquid

For a ring wetted by a liquid, see Fig. (12);

F=W+

F=W+ ( )………………….. (1.21)

Equ. (1.21) is usually used to measure ( ). The weight (W) is usually negelcted.

Examples

Example (1.1): The weight of the cylinder shown in the figure is (W) and its radius of

gyration is (KG). The cylinder rotates at angular speed (N). Develop an expression for

viscosity of oil ( ) required to stop the cylinder in (10) seconds.

Sol.:

T= T1+T2

T1= F*R=

∴ T1=

dT2=

∴ T2 =∫

0

∴T=

0

Fig. (11)

𝐹𝜎

Fig. (12)

𝐹𝜎0

𝐹𝜎

𝐹𝑝

Page 26: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 26

Example (1.2): Derive an expression for the torque (T) required to rotate the circular cone

shown in the figure at a rate of (ω), in terms of the related variables ( , ω, and R).

Sol.:

dF=

=

=

( )

dF=

dT=dF*r

=

T=∫

0

=

∴T=

Example (1.3): A reservoir of glycerin has a mass

of (1200 kg) and have a volume of (0.952 m3). Find the glycerin weight, density, specific

weight and specific gravity.

Sol.:

W=mg=1200*9.8 W=11770 N

= 00

0 =1261 kg/

=

0

0

= =1261*9.8

Example (1.4): Convert (15.14 Poise) to kinematic viscosity in ( ) if the liquid has

a specific gravity of (0.964).

Sol.:

=s =0.964*1000 =964 kg/

γ = 12360

N/𝑚

sin𝜃

𝑟 𝑠𝑖𝑛𝛽

β

β

𝜃

𝜃 𝜇

𝜇

𝑟 𝑠𝑖𝑛𝛽

𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑐𝑜𝑛𝑒

𝜃

Page 27: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 27

15.14P *

0

( )

Example (1.5): The bulk modules of elasticity of water is (2.2 GPa), what pressure is

required to reduce its volume by (0.5 percent).

Sol.:

k=-

2.2*109=

0 0

0 00

Example (1.6): A small circular jet of mercury (0.1 mm) in diameter issues from an

opening. What is the pressure difference between the inside and outside of the jet? Use

( N/m)

Sol.:

p*DL=2

Thus

p=

0

0 0

Problems

The problems number listed in the table below refer to the problems in the

"textbook", Chapter "1”;

Article No. Related Problems

1.4 1,2,3,5,14,15,16,17,22

1.5 7,9,11,12,28,39,42,43,46,47

Page 28: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 28

Chapter -2-

Fluid Statics

2.1 Introduction

In static fluids, no relative motion between the fluids particles exist, therefore no

velocity gradients in the fluid exist, and hence no "shear stresses" exist. Only "normal

stresses (pressure)" exist. In this chapter, the pressure distribution in a static fluid and its

effects on surfaces and bodies submerged or floating in it will be investigated.

2.2 Pressure Variation in a Static Fluid

The pressure (p) in a static fluid may change with space coordinates (x, y, z) and

with direction ( ).Thus, to find the differential change in pressure (dp) in a static fluid, we

may write;

p= p (x, y, z, )

…….… (2.1)

To derive the differential equation for the pressure (p),

we have to derive an expressions For the partial

derivatives (

) in equation (2.1),

Which represents the changes in pressure with (x, y, z and ), see Fig. (1).

2.2.1 Pressure Variation with Direction

The pressure at a point in a static fluid acts with the

same magnitude in all directions. This physical fact will

be proved mathematically by taking a fluid element of

tetrahedron shape, see Fig. (2). we will apply Newton's

2nd

law in the three directions, knowing that;

Where l, m, n = direction cosines

+ ∑

Fig. (1)

𝑝𝑥 yz l ne ( re δAx)

𝑝𝑦 xz l ne ( re δAy)

𝑝𝑧 xy l ne ( re δAz)

𝑝 l ne ( re δA)

Fig. (2)

Page 29: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 29

+ ∑

+ ∑

Thus; independent of direction

If we take the limit as [( ) ], the element approaches a "point", thus, the

above result applies for a point in a static fluid, that is the pressure is independent of

direction, and hence;

………………. (2.2)

2.2.2 Pressure Variation in Space

To find the pressure variation in a static fluid with space coordinates (x, y, z), a

cubical fluid element will be studied, see Fig. (3). The pressure (p) at the center of the

element is assumed to change with the three coordinates and we want to find the rate of

changes (

). The Newton's 2

nd law is applied for the element of Fig. (3).

H.O.T (Higher Order Term)

Fig. (3)

(𝑝 𝜕𝑝

𝜕𝑦

𝑑𝑦

)𝑑𝑥 × 𝑑𝑧

(𝑝 𝜕𝑝

𝜕𝑧

𝜕𝑧

)𝑑𝑦𝑑𝑥

(𝑝 𝜕𝑝

𝜕𝑥

𝑑𝑥

𝑧)𝑑𝑦𝑑𝑧

)

d

(𝑝 𝜕𝑝

𝜕𝑦

𝑑𝑦

)𝑑𝑥𝑧 (𝑝

𝜕𝑝

𝜕𝑧)𝑑𝑦𝑑𝑥

(𝑝 𝜕𝑝

𝜕𝑥

𝑑𝑥

)𝑑𝑦𝑑𝑧

0

𝑝(𝑥 𝑦 𝑧)

Page 30: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 30

+∑

(

) (

)

Or;

Since

…………………….. (2.3)

+ ∑

(

) (

)

= 0 ………………………. (2.4)

Equations (2.3) and (2.4) indicate that no changes in pressure occur in the

horizontal xz- plane, i. e., all points in the same horizontal plane in a static fluid have

the same pressures.

+ ∑

(

) (

)

Or;

………………………………………. (2.5)

Equation (2.5) indicates that the pressure in a static fluid decreases as (y), the

vertical coordinate, increases. This is a logical result physically, since the increase in (y)

means decease in the fluid column height which causes the pressure.

2.2.3 Basic Hydrostatic Equation

This equation is obtained by substituting equations (2.2), (2.3), (2.4) and (2.5) into

equation (2.1). Thus;

0

Equ. (2.3)

Equ. (2. )

γ Equ. (2.5)

0 Equ. (2.4)

Page 31: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 31

Hence: y

Or;

This is the basic differential equation whose integration gives the pressure

distribution equation in a static fluid. The integration depends on how the specific weight

( ) vary with the vertical coordinate (y). Accordingly, the distribution for

incompressible and compressible fluids is different.

2.2.4 Pressure Variation for Incompressible Fluids

For incompressible fluids, ( =constant), and hence ( = constant), and the

integration of equ. (2.6) yields;

∫ ∫ y

y n

Or; y n

The ( n ) of integration is the same

for any two points. (1) and (2), thus;

y y

y

If we use the coordinate (h = -y) measured vertically downward, i. e.,

(h = -y2), then see Fig (4);

…………………………… (2.7)

As mentioned previously, the pressure increases as we move downward (+h) and

decreases as we move upward (-h).

2.2.5 Pressure Variation for Compressible Fluids

For compressible fluids, the density ( ) changes with temperature (T) as the perfect

gas law (p = RT) indicates. And since the temperature (T) varies with altitude (y), the

density ( ) also changes with (y), and accordingly ( ) changes with (y) also. Thus;

………………….. (2.8)

Basic Hydrostatic Equation …………………. (2.6)

0 (y1=0)

Fig. (4)

Page 32: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 32

Hence, equ. (2.6) becomes;

……………… (2.9)

To integrate this equation, we must know how (T) varies with (y). For this purpose, the

atmosphere is divided into two layers;

I - Troposphere: (from sea level up to 10769m)

0 ( 0) …………………. (2.10)

Where: 0= Reference temperature at seal eve ( 0 ) = 288k

= Lapes rate = -0.00651 ˚C/m = -0.00357 ˚F/ft

Thus, equ. (2.9) becomes;

( )

Integrate from ( )where( ), to ( ) where( ). Thus:

( )

………………. (2.11)

II - Stratosphere: (from y = 10769 m up to 32 km)

( y r e ) …….... (2.12)

Thus:

And hence:

( )

……………. (2.13)

( ) is the pressure at ( )

2.3 Pressure Measurements

2.3.1 Absolute and Gage Pressures

The absolute pressure ( ) is the pressure measured relative to a complete

vacuum (zero absolute pressure), whereas the gage pressure ( ) is the pressure

measured relative to the local atmospheric pressure ( ) ).The local atmospheric

pressure may be larger than, smaller than are equal to standard atmospheric pressure

( ) ) which is a constant value, see Fig. (5). Thus;

Page 33: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 33

) ………………… (2.14)

2.3.2 Atmospheric Pressure Measurement

The "barometer" is usually used to measure the atmospheric pressure. It consists of

a glass or Perspex tube with one open and immersed in a bath of mercury, see Fig. (6). the

pressure at the free surface is ( ), which is equal to the pressure at point 2 ( ) (see

equs. (2.3), and (2.4)). Thus, using equ. (2.7) ( );

…………………….. (2.15)

The vapor pressure of mercury is very small and can be neglected,

hence;

………………………………. (2.16)

And;

……………………….. (2.17)

If ( ) ), then (h = 76 cm). The mercury is used because its specific weight is

large and thus (h) will be small and reasonable. Also the vapor pressure is very small and

can be neglected.

"Aneroid Barometer" is also used to measure the

atmospheric pressure, see Fig. (7). It measures the

difference in pressure between the atmospheric pressure

( ) and an evacuated cylinder by means of a sensitive

elastic diaphragm and linkage system.

Fig. (5)

Fig. (6)

Fig. (7)

Pabs=0

Absolute zero

(Complete Vacuum)

𝑝𝑎𝑏𝑠 𝑝𝑎 1.01325bar

76 cmHg 10.34mH2o

1 atmosphere

14.7 psi(𝑙𝑝𝑓

𝑖𝑛 )

2116 psf (𝑙𝑝𝑓

𝐹𝑡 )

29.92 in Hg 33.91 ft H2o

Page 34: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 34

2.3.3 Gage Pressure Measurements

2.3.3.1 Bourdon Gage

The "bourdon gage" shown in Fig. (8) is a typical

of the devices used for measuring gage pressure. The

pressure element is a hollow, curved, flat metallic tube

closed at one end; the other end is connected to the

pressure to be measured. When the internal pressure is increased,

the tube tends to straighten, pulling on a linkage to which is attached a pointer and causing

the pointer to move. The dial reads zero when the inside and outside of the tube are at the

same pressure, regardless of its particular value. Usually, the gage measures pressure

relative to the pressure of the medium surrounding. The tube, which is the local

atmosphere. According to equ. (2.7); the pressure recorded by the gage of Fig. (8) is;

…………………….. (2.18)

…………………….. (2.19)

2.3.3.2 Pressure Transducers

The devices work on the principle of conversion pressure energy to mechanical

energy, then to electrical signals, sees Fig. (9).

2.3.3.3 Manometers

Manometers are devices that employ liquid columns for determining difference in

pressure. They are usually made of glass (or PVC) tubes filled of one or more liquids with

different specific gravities and that are not miscible in each other. Each manometer has

tow ends. The general procedure that should be followed in working any manometer

problem is as follows;

Fig. (8)

Fig. (9)

Fig. (8)

Page 35: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 35

1. Start at one end (or any meniscus if the circuit is continuous) and write the pressure

there in an appropriate unit or in an appropriate symbol if it is unknown.

2. Add to this the change in pressure, in the same unit, from one meniscus to the next

(plus if the next meniscus is lower, minus if higher).

3. Continue until the other end of the gage (or the starting meniscus) is reached and

equate the expression to the pressure at that point, known or unknown.

2.3.3.3.1 Piezometer

This type of the manometers, illustrated in Fig. (10),

is used to measure the pressure in a liquid when it is above zero

gage. Using equ. (2.7);

h (Pa)

= ( ) ................… (2.20)

( ) .................… (2.21)

Piezometer would not work for negative gage pressure, because air would flow into

the container through the tube. It is also impractical for measuring large pressures at A,

since the vertical tube would need to be very long.

For measurement of small negative or positive gage pressures, the tube may take

the form shown in Fig. (11). For this arrangement;

( )

= ( )

( ) (2.23)

( )( )

For greater negative or positive gage pressure, a second

liquid of greater (s) is employed, see Fig. (12).

=

Fig. (11)

Fig. (12)

……….. (2.22)

……….. (2.24)

……….. (2.25)

Fig. (10)

Page 36: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 36

Fig. (13)

2.3.3.3.2Differential Manometer

This type of manometers (Fig. (13)) determines the difference in pressure at two

points A and B. the equation of this monometer is:

Or;

( ) .… (2.26)

And;

(Units of length of ) .... (2.27)

Equation (2.26) represents the difference in both absolute and gage pressures at A and B.

2.3.3.3.3 Micromanometers

This type of manometers are used for measuring

small pressure differences, see Fig . (14). The small

difference ( ) at C.S.A.(A) is magnified to a

large difference (R/2) at smaller C.S.A.(a).

The manometer equation is;

( ) (

)

(

) ( )

But; A

Thus, we can show that:

* (

)

+ ……… (2.28)

2.3.3.3.4 Inclined Manometer

The inclined manometer (Fig. (15)) is

frequently used for measuring small difference

in gage pressure. It is adjusted to read zero, by

moving the inclined scale. Since the inclined tube

requires a greater displacement of the meniscus

for given pressure difference than a vertical tube,

𝑠 𝛾

𝑠 𝛾

𝑠 𝛾

Fig. (14)

𝑠 𝛾

𝑦

Fig. (15)

𝑠

𝛼

Page 37: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 37

it offers greater accuracy in reading the scale. The equations of the manometer are;

( )

Thus;

( )

but h=R sin

and A

Thus;

( n

) ………………. (2.29)

The device is usually designed so that the angle ( ) can be changed to more than one

value.

Note:

The value of pressure (p) can be converted to columns of any fluid by the following

relation;

p =

Thus;

Unit length of fluid 1

Unit length of fluid 2 ............………..... (2.30)

Unit length of fluid 3

2.4 Hydrostatic Forces on Submerged Surface

Hydrostatic forces excreted by a static fluid are always perpendicular to the surface

on which they act.

2.4.1 Horizontal Surfaces

A plane surface in a horizontal position in a fluid at rest is

subjected to a constant pressure ( p = ), see Fig.(16). To find the

resultant hydrostatic fore (F), consider an element (dA), on which

an element force (dF) acts;

dF = pdA = A

Thus; F = ∫ ∫ A ∫ A

Fig.(16)

Page 38: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 38

Hence;

F= A A ... (2.31)

Center of Pressure C.P. ( )

It is the point through which the resultant hydrostatic force (F) passes. To find the

coordinates of center of pressure ( ), take moments about x & y coordinates;

F*x = ∫

A x ∫ ∫x A

Hence; x

∫ x x

F * y ∫

y ∫ ∫y A

Hence; y

∫ y

Hence; C.P. = C

(x y ) = (x y) [for horizontal surfaces only] …………...(2.32)

2.4.2 Inclined Surfaces

For inclined plane surfaces, the pressure (p= ) varies anlog the surface, since (h)

is not constant, see Fig. (17). For element (dA), the force acting on it (dF) is;

𝑦 n𝛼

h= y sin 𝛼 Fig. (17)

p= 𝛾

𝑝𝑐= 𝛾

If (𝛼 °)(vertical surfacse) → h=y ; =𝑦

∇ α

Page 39: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 39

dF= pdA= n

F=∫ ∫ y n n ∫ y n A y n

Hence;

F = ………….... (2.33)

To find the center of pressure (x y );

F * y = ∫

y n y ∫ n

Thus; y

Where = second moment of area (A) about horizontal axis (ox).

From the parallel axis theorem;

Where Second moment of area (A) about horizontal centroidal axis (cx).

= Distance between the two axes (ox) & (cx)

Thus;

y

………………….. (2.34)

F * x = ∫

y n x ∫ n

Thus; x

Where;

= Product moment of area (A) about axes (ox & oy)

= Product moment of area (A) about centroidal axes (cx & cy)

= (parallel axis theorem)

Thus;

x

............................……………….... (2.35)

When x or y or both are axes of symmetry, then ( ) & (x )

Page 40: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 40

The Pressure Prism

It is a prismatic volume with its base the given surface area and with altitude at any

point of the base given by (p = ), see Fig. (18)

dF = pdA = A

F= ∫ ∫ …………...... (2.36)

Thus, the volume of the pressure prism equals the

magnitude of the resultant force acting on one side of the surface.

To find cent of pressure;

F * xP ∫ x

∫ ∫

Similarly, we can show that;

i.e. C.P. = C of volume

( ) ……..…………... (2.37)

2.4.3 Curved Surfaces

When the elemental force (dF = pdA) vary in direction, as in curved surfaces, they

must be added as vector quantities; i.e., their components (horizontal and vertical) are

added vectorially. In Fig. (19), the force (dF) on an element (ds) of the curved surface is

replaced by its two components, horizontal (dFH) and vertical (dFV).

Fig. (19)

Horizontal Component (FH)

The horizontal component of pressure force on a curved surface is equal to the

pressure force exerted on a projection of the curved surface. The vertical plane of

projection is normal to the direction of the component

Fig. (18)

𝛾 𝐴

𝛾 𝐵

γ

Page 41: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 41

dF = pdA =

dFH = dF sin n

Thus; FH= ∫ ∫ ............… (2.38)

Where;

Vertical projection of the curved surface on a vertical plane

Centroid of ( ) distance to the free surface

…..… (2.39)

………… (2.40)

Equations (2.38), (2.39) and (2.40) are similar to equations (2.33), (2.34) and (2.35) for

inclined surfaces, with ( °), i.e., vertical surface, which is the vertical projection

( ) of the curved surface.

Vertical Component (Fv)

The vertical component of pressure force on a curved surface is equal to the weight

of liquid vertically above the curved surface and extending up to the free surface;

d y y x

Thus; ∫ ∫ ……………… (2.41)

Where;

l e l en l e e een e r e r e n e ree r e

i.e.;( ) ( )

( ) ( ) .........…………….……... (2.42)

Note;

When the liquid is below the curved surfaces, see Fig. (20), and the pressure

magnitude is known at some point o (p0), an "imaginary" or equivalent free surface (I.S.)

Page 42: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 42

can be constructed (

) above (o). The direction of force ( ) is reversed to obtain the

real fore (F). The resultant of ( ) and ( ) is found as;

F = √

=

......................…(2.43)

2.5 Buoyancy

The buoyant force ( ) is the resultant force exerted on a body by a static fluid in

which it is submerged or floating. Its magnitude is equal to the weight of the displaced

volume. It acts vertically upward through the center of buoyancy (B) which is the centroid

(C) of the displaced volume. To prove the above statements mathematically, consider the

body shown in Fig. (21). the body has 6 curved surfaces, on which 4 horizontal forces

(F1,F2, F3 andF4) and 2 vertical forces (F5 andF6) are acting. To find the resultant of these

forces;

=

= 0 (since )

=

= 0 (since )

-

R = √

Thus : ................................ (2.44)

To find the center of buoyancy (B), take moments;

Fig. (20)

𝑝𝑜 γ

Fig. (21)

Page 43: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 43

∫ x ∫

Similarly, we can show that

Hence; ( ) ( )

( ) ( ) …………………................ (2.45)

Notes:

1- When the body is submerged in two fluids, then the buoyant force ( ) is the sum of

the two buoyant forces exerted by the two fluids, see Fig. (22)

=

2- When the body is floating, only the submerged volume is used in calculating ( ), see

Fig. (23)

Thus;

l l e y

l e l e

y e e

3- To find the volume ( ) and weight (W) of an oval - shaped body, it is weighted in two

fluids ( ), see Fig. (24)

W=

=

Weight of body in fluid 1

Weight of body in fluid 2

Fig. (22)

Fig. (23)

Fig. (24)

Page 44: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 44

2.5.1 Hydrometers

They are devices that use the principle of buoyant force to determine the specific

gravity (or relative density) s of liquids. Fig. (25) shows a hydrometer in two liquids. It

has a stem of prismatic cross section of area (a).

In fluid 1 : W =

In fluid 2 : W = ( )

Hence, we can show that.

……………….. (2.46)

Where ( = Submerged volume in fluid 1 )

Note:

1. Equation (2.46) is used to divide the scale of the stem after specifying the geometry

and weight of the hydrometer.

2. Hydrometer is made usually from a glass or Perspex tubes. If the weight of these tubes

do not satisfy the hydrometer equation (W = ), then additional weight, such as mud,

lead, is added inside the bulb.

3. For each hydrometer, there are minimum and maximum values of (s) which can be

measured by its scale.

2.6 Stability of Submerged and Floating Bodies

2.6.1 Submerged Bodies

A completely submerged (immersed) object has a "rotational stability” when a

restoring couple is set up by any small angular displacement. This occurs only when the

center of gravity (G) is below the center of buoyancy (B), see Fig. (26)

Rotational Stability

Fig. (26)

Fig. (25)

Page 45: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 45

2.6.2 Floating Bodies

I- Liner Stability; A floating body has a linear stability when a small liner displacement

in any direction set up restoring force tending to return it to its original position. A

small upward displacement decreases the volume of liquid displaced, resulting in an

unbalanced downward force, and small downward displacement results in greater

buoyant force, which causes an unbalanced upward force.

II- Rotational Stability; Any floating object with G below B floats in stable equilibrium.

Certain floating objects, however, are in stable equilibrium even when G above B.

This may occurs when the line of buoyant force after the heel intersects the center line

above G, at a point called the "Metacenter M", see Fig. (27), which is a prismatic

body (all parallel cross – sections are identical). When the body is displaced by angle

( ) clockwise, a counter clockwise restoring couple is set up, whose value is;

Restoring Couple = W * MG sin ..................…. (2.27)

Fig. (27)

The distance (MG) is called the "Metacentric Height", and it is direct measure of the

stability of the body. The following criteria are used for this purpose;

MG > 0 {M above G} Stable Equilibrium

MG < 0 {M below G} Unstable Equilibrium ……… (2.48)

MG = 0 {M and G coincides} Neutral Equilibrium

For a general floating body of variable cross- section, such as a ship, a convenient

formula can be developed for determination of the metacetic height (MG). This will be

done in the next article.

Page 46: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 46

2.6.3 Metacenter

The (Metacenter M) is the intersection of the buoyant force after the angular

displacement and the original center line; or, it is the intersection of the lines of action of

the buoyant forces before and after the heel (angular displacement).

In what follows, we will derive a formula for determining the Metacentric height (MG).

This will be done for a ship, which is a non – prismatic body (parallel cross – sections are

not identical), see Fig. (28). The results are, however, general and can be used for bodies

with prismatic cross – sections.

The Metacentric height (MG) is found as;

MG = MB

BG . ………….… (2.49)

(-) sign is used when G above B

(+) sign is used when G below B

Now; MB =

……………………………. (2.50)

Where; x= Centroidal distance of the displaced volume after the heel (B')

To specify (x), we take moments of volume about the line (0-0);

( ) ( ) ( ) ( )

( ) ( ) ( ) ( )

( ) ( )

=∫

Fig. (28).

𝛼 𝑥

o

o

Page 47: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 47

=∫

But d =x tan dA

Thus; x =∫

n A

And, hence;

x =

∫ A n

…………………………… (2-51)

Where: ∫ Second moment of area of water line surface about longitudinal

axis (o-o)

= Displaced (submerged) volume

Thus, (2.51) in (2.50) gives;

MB =

……………………….. (2.52)

And hence (2.52) in (2.49) gives

MB =

……………………….. (2.53)

After calculating (MG) from equ. (2.53), the criteria specified in equ. (2.48) is used to

specify the state of equilibrium of the body.

2.7 Relative Equilibrium

In this application, the fluid is in motion such that no layer moves relative to an

adjacent layer; as a result, the shear stresses throughout the fluid are zero (absent), which

is the same as in fluid statics. Therefore, the laws of fluid static are applied for this type of

motion. Examples are;

1. A fluid moves with uniform velocity

2. A fluid moves with uniform linear acceleration

3. A fluid with uniform rotation

2.7.1 Uniform Linear Acceleration

A liquid in an open vessel is given a uniform linear acceleration (a=axi+ayj), see

Fig. (29). After some time the liquid adjusts to the acceleration so that it moves as a solid;

i.e, the distance between any two fluid particles remains fixed, and hence no shear stresses

occur. We will apply Newton's 2nd

law to find the pressure gradients and distribution

Page 48: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 48

Fig. (29)

∑ x

(p

) (

)

…(2.54)

∑ y=m

(p

) (

)

Thus;

( +g) …………………………. (2.55)

Equations (2.54) and (2.55) will reduce to equations (2.3) and (2.5) if (ax=0 and ay=0)

respectively. Now, to find the change in pressure;

dp =

dp = - ( ) …………………………… (2.56)

The angle of inclination ( ) for the lines of constant pressure can be found from

equ. (2.56) by setting (dp=0); thus;

0 = ( ) y

Hence;

………………….. (2.57)

Equation (2.56) can be integrated with B.C. (p= 0 at x=0, y=0) to obtain;

p = 0 ( ) ………………….. (2.58)

)p+𝜕𝑝

𝜕𝑦

𝑑𝑦

)𝑑𝑥

)p-𝜕𝑝

𝜕𝑥

𝑑𝑥

)𝑑𝑦 )p+

𝜕𝑝

𝜕𝑥

𝑑𝑥

)𝑑𝑦

)p-𝜕𝑝

𝜕𝑦

𝑑𝑦

)𝑑𝑥

dw=𝜌𝑔𝑑𝑥𝑑𝑦

Page 49: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 49

Equation (2.55) can be integrated in analogous way to equ. (2.7), to obtain the following

formula;

= + ( ) …………………………. (2.59)

Again, for (ay=0), equ. (2.59) reduces to equ. (2.7) For static fluids

Note; For open tanks ( 0 ) and point (o) is at the middle (center) of the width of

the tank. For closed tanks ( 0 ) and point (o) is not at the middle (center) of the

width.

1.7.2 Uniform Rotation

Rotation of a fluid, moving as a solid, about an axis is called" Forced Vortex

Motion". Every particle of the fluid has the same angular velocity. This motion is to be

distinguished from" Free-Vortex Motion", in which each particle moves in a circular path

with speed varying inversely as the distance from the center. A liquid in a container, when

rotated about a vertical axis at constant angular velocity ( ), see Fig (30), moves like

solid after some time interval. No shear stresses exist in the liquid, and the only

acceleration that occurs is directed radially inward towards the axis of rotation (an=

and ) Thus, analogous to equations (2.54) and (2.55), we can wirte;

( ) ………….. (2.60)

( ) …………… (2.61)

The pressure distribution analogous to equ. (2.58) will be;

= 0+

( ) ……………..(2.62)

For points along the horizontal plane (y=0), equ.(2.62) gives;

0

0

……………..(2.63)

Which gives the distance to the free surface.

In a similar way, equ. (2.61) can be integrated to obtain;

= + ( ) ………………………. (2.64)

Where: h= Vertical downward distance from the free surface

Fig. (30)

Page 50: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 50

Note:

1. Lines of constant pressure are of parabolic type.

2. Volume of the parabola =

(Volume of cylinder with same base and height)

3.

0

0

Thus; z =

Examples

Example (2.1): For the system shown in the figure, calculate the manometer reading (H).

Sol.:

60000+0.2 13.6 0.92 =16000

H= 0000 0 0 0 000

∴ 0.3242 m= 32.42 cm

Example (2.2): Determine the pressure difference between the water pipe and the oil pipe

shown in the figure, in Pascals and in meters of water.

Sol.:

0

0 ( )

∴ 0

0 0

0 O

Example (2.3): If the weightless quarter cylindrical gate shown in the figure is in

equilibrium, what is the ratio between ( ) and ( )?

Sol.:

F= hA=

R=

Page 51: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 51

= =

F*(R- )= ( )

Example (2.4): For the two-dimensional weightless solid body shown in the figure,

determine the magnitude and direction of the moment (M) applied at the pivot required to

hold the body in the position shown in the figure.

Sol.:

= =9810*1*2=19620 N

y

1.332 m

=

30819 N

0.849 m

F= =9810*1*2.828=27746.9 N

=1.414+ ( )

=1.885 m

∑ =0

F*0.47+

∴M=13078 N.m

Page 52: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 52

Example (2.5): A (2cm) diameter cylinder of wood (s=0.5) floats in water with (5 cm)

above the water surface. Determine the depth of submergence of this cylinder when placed

in glycerin (s=1.25). Will it float in stable, unstable or neutral equilibrium in this case?

Sol.:

In water: W=

( 5)

Thus ; h=10 cm

In glycerin:

∴ x=4 cm

5cm , =2cm

00=

MG= 00

cm

< ∴Unstable Equilibrium

Example (2. 6): Calculate the weight and specific gravity of the object shown in the

figure to float at the water-oil interface as shown.

Sol.:

W=

=

( )

( )

=

=9810*0.00159

∴W=15.6 N

s= ⁄

=

( 0 )

0 =

000

∴s=0.899

Page 53: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 53

Example (2.7): The cylindrical vessel shown in the figure is rotated about its vertical

longitudinal axis. Calculate:

1. The angular velocity at which water will start to spill over the sides.

2. The angular velocity at which the water depth at the

center is zero, and the volume of water lost for this case.

Sol.:

(a)

∴ H = 2z = 150mm

H =

=0.15

(

)

∴ = 34.4 rad/sec

(b) H'= (

)

0.3=

(0 )

rad/sec

=1.178*10

-3 m

3

Example (2.8): An open cylindrical tank (0.9m) high and (0.6m) in diameter is two –

thirds filled with water when it is stationary. The tank is rotated about its vertical axis,

calculate:

1. The maximum angular velocity at which no water is to spill over the sides.

2. The angular velocity at which the bottom of the tank is free of

water for a radius of (150mm).

Sol.:

a- H =

*0.9 = 0.6m

∴ m

Page 54: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 54

( )

∴ =11.43 rad/sec

b- z-

( )

( )

W = 16.16 rad/sec

Example (2.9): For the closed rectangular tank shown in the figure, calculate the pressure

at points (A) and (B), and the forces on sides (AB) and (CD).

Sol.:

tan =

0 º

tan

………………..(1)

…………………….. (2)

(1)& (2) gives:

y = 0.814 m and x =1.77 m

p2=p1+ (ay+g) h

=140000 + 0.68*1000(0 + 9.8) h

Thus; p2 =140000 + 6670.8h

z = 2.4 tan z = 0.288 m

pA = 140000 + 6670.8*z pA = 141.92 kPa

pB = 140000 + 6670.8*(1.2 + z) pA = 149.93 kPa

To calculate the hydrostatic forces, we have to imagine a free surface at which (p=0 gage)

above the existing surface at which (p=140 kPa):

Z' = 0000

0 0 z' = 21m

FAB= hA=0.68*9810*(0.6+z+z')*1.2*1.5 FAB=262.6 kN

FCD= hA=0.68*9810*(0.386+z'-0.6)*1.2*1.5 FCD=249.6 kN

A

B

D

Page 55: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 55

Problems

The problems number listed in the table below refers to the problems in the

"textbook", chapter"2".

Article

No. Related Problems

2.2+2.3 4,5,7,10,13,14,16,20,21,22,24,26,29,30,31,32,33,34

2.4 36,37,39,40,44,45,46,53,59,60,61,62,63,65,68,69,71,78,79,82,8

6,89,91,101,106

2.5+2.6 92,93,96,97,98,100,102,103,105

2.7 110,112,114,115,116,117,118,122,123,124,126

Page 56: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 56

Fig. (1)

Chapter -3-

Fluid Flow Concepts

3.1 Definitions and Concepts

Velocity (V): It is the time rate of change of displacement of fluid particles. It is a vector

quantity:

( )

.................... (3.1)

Acceleration ( ): It is the time rate of change of velocity vector.

( )

( )

Thus;

a=

And;

Where;

Streamline (S.L.): It is an imaginary line or

curve drawn in the fluid flow such that the

tangent drawn at any point of it indicates the

direction of velocity ( ) at that point. Since the

Local

Acceleration

Total

Acceleration

Convective Acceleration

…………..(3.2)

Page 57: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 57

Fig. (2)

Fig. (3)

velocity vector has a zero component normal to streamline, there can be no flow across a

streamline at any point, see Fig.(1). Streamlines indicate the direction of motion in

various sections of fluid flow.

Types and Classification of Flow

1- Internal and External Flow

Internal Flow; is bounded by a wall (surface) around all the

circumference of flow. Examples are pipe or duct flows, flows

between turbine or compressor or pump blades see Fig (2).

External Flow; is bounded by a wall (surface)

from one side and free at other sides. Examples are

flow over a flat plate, over airfoil, over a car, over

airplane fuselage, see Fig. (3).

2- Steady and Unsteady Flow

Steady Flow; none of the flow and fluid variables (velocity, acceleration, density.....)

vary with time.

Unsteady Flow; any one of the variables change with time

Steady Flow: ( )

Unsteady Flow: ( )

3- Uniform and Non – Uniform Flow

Uniform Flow; velocity vector ( )remains the same at all sections of the flow.

Non - Uniform Flow; velocity vector ( ) changes from section to sections of the flow.

Uniform flow;

Non - Uniform flow;

𝑢∞ 𝑢∞

….................... (3.3)

s=space .........................(3.4)

Page 58: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 58

Fig. (4)

Fig. (5)

Fig. (6)

Fig. (7)

4- Laminar and Turbulent Flow;

Laminar Flow; fluid particles move in smooth paths in layers or laminas with one layer

sliding over an adjacent layer. The paths of

individual particles do not cross or interact see

Fig.(4). Laminar flows occur at low velocities (low

Reynolds number Re) , where (Re =

) ; =

characteristic length.

Turbulent Flow; paths of various particles are irregular and random with no systematic

pattern of flow see Fig.(5). Turbulent flow occurs at high velocities (high Re). In

turbulent flow, the velocity (u) fluctuates with time. The time average velocity ( ) can be

found as, see Fig. (6);

0

where;

u = Instantaneous velocity

= Fluctuation from the mean value

T= Time period

Note: For pipe flow; Re < 2000 Laminar Flow

Re > 4000 Turbulent Flow

5- One, Two - and Three - Dimensional Flow

One - Dimensional (1-D) Flow; the variation of

fluid and flow parameters transverse to the main

flow are absent. These parameters remain constant

at any cross - section normal to the main flow see

Fig.(7). Mathematically;

( ) ................................ (3.6)

……………….(3.5)

Page 59: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 59

Fig. (8)

Fig. (11)

Fig. (9)

Fig. (10)

Two Dimensional (2- D) Flow; the variation in the

flow and fluid parameters takes place in x- and y-

directions only see Fig.(8). This means that all the

particles move in parallel planes (x-y planes) along

identical paths in each plane. there is no variation

normal to this plan. Mathematically;

( ) ........................................(3.7)

Three - Dimensional (3-D) Flow; the flow and fluid

parameters have variation in all the three directions,

See Fig.(9).Mathematically;

( ) ......................................(3.8)

6- Viscous (Real) and Non- Viscous (Ideal) Flow

Viscous (Real) Flow; effects of viscosity exist and

cause reduction of velocity inside the boundary-

layer (b.l.)

Non - Viscous (Inviscid, Ideal); effects of viscosity

are absent outside the (b.l.), see Fig.(10).

7- Incompressible and Compressible Flow

Incompressible Flow; the flow in which the density ( ) is assumed constant

( = constant ). Examples are flow of liquids and gases with low velocities (M ).

Compressible Flow; the flow in which the density ( ) is not constant, but varies with

pressure and temperature. Examples are gas flow and special types of liquid flow (such as

water hammer phenomena).

Volume Flow Rate (Q) and Mass Flow Rate ( )

Volume Flow Rate(Q); is the volume rate of fluid

passing a section in a certain fluid flow. Thus (see

Fig. (11));

Page 60: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 60

Fig. (12)

Q=

Or

Q= A.V = AV A V

..........................(3.9)

Where;

A=Cross - sectional area of the flow.

V= Average velocity of the flow.

A.V =AV cos = AV cos(0) =AV

Mass Flow Rate ( ) ; is the mass rate of fluid passing a section in a certain fluid flow;

Or; kg/s ……….....(3.10)

If the velocity (V) is variable across the section, then;

Q= ∫

…………..... (3.11)

= ∫

…………..... (3.12)

EX: For laminar flow through pipes, the

velocity distribution across the section is given

by;

(

) , see Fig. (12)

Thus;

Q = ∫ ∫ ( (

)

) ×

0

Hence; Q =

= AV, where V= average velocity

The average velocity (V) can be calculated as;

V =

∫ ( (

)

) ×

= ∫

Page 61: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 61

Fig. (13)

System (sys)

It is a quantity of matter of fixed mass and identity. the system boundaries may be

fixed or movable. System exchanges energy only with the surrounding

Control Volume (C.V.)

It is a fixed region in the space bounded by the control surface (C.S.). The control

volume (C.V.) can exchange both mass and energy with the surrounding.

Note; System approach is usually used in solid mechanics, where the body is clearly

identified and can be followed during its motion. In fluid mechanics, a "system" of fluid

cannot be easily followed during its motion, since its boundaries are not clear. Instead, a

“control volume" approach is used, where a fixed volume specified in the fluid is

considered and the changes in this c.v. due to flow of fluid system through it is studied.

3.2 General Control Volume Equation

The general control volume equation, which will be derived in this article, relates

the changes in a general property of the "System" (Mass, Energy, Momentum) to that

occurred in a “Control Volume" through which the system flows, see Fig. (13).

Let;

N = Total amount of a general property within the system (mass, momentum, energy)

And;

= The amount of (N) per unit mass (N/m)

Page 62: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 62

Thus;

N = m = = ∫ ∫

And;

= ∫

Now, the rate of change of (N) within the system is;

l

0

) )

l

0

(∫ ∫

)

(∫

)

By adding and subtracting the term(∫

) ;

l

0

(∫ ∫

)

(∫

)

l 0

(∫ ∫

)

= l 0 ) )

l 0

( )

=

=

∫ ∫

=

∫ ∫

Hence, the final form of the “General Control Volume Equation“ is;

∫ ∫

...................... (3.13)

Equation (3.13) will be used to derive FOUR laws of conservation that are used to

analyze any fluid flow problem. These are:

1- Law of Conservation of Mass: Continuity Equation (C.E.)

2- Law of Conservation of Energy: Energy Equation (E.E.)

3- Law of Conservation of Liner Momentum: Momentum Equation (M.E.)

4- Law of Conservation of Angular Momentum: Angular Momentum Equation.

Page 63: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 63

Fig. (14)

3.3 Law of Conservation of Mass: Continuity Equation (C.E.)

The property (N) is the mass (m) of the system. Thus;

N= m

[ mass cannot be created nor can be destroyed]

Thus; from equ.(3.13);

∫ ∫

General C.E. ......….…….... (3.14)

For the flow control volume shown in Fig.(14);

( ) ( )

( ) ( )

=

Hence, equ.(3.14) can be written as;

.......………... (3.15)

For steady flow, (

), thus;

C.E. for steady flow …………………..(3.16)

For incompressible flow ( ), hence;

C.E. for steady incompressible flow ………..(3.17)

3.3.1 Continuity Equation at a Point

To derive the continuity equation at a point, not for a C.V. (equ.3.15), we will

apply this equation for an infinitesimal cubic element of fluid, see Fig.(15).

Page 64: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 64

Using equ.(3.15) ;

+(

) (

)

Substituting for each term and simplify, it is obtained;

( )

( )

( ) General C.E. at a point ……….(3.18)

For incompressible flow ( )

=0,

Thus, equ.(3.18) becomes;

+

C.E. at a point for incompressible flow …………………(3.19)

3.4 Law of Conservation of Energy: Energy Equation (E.E.)

The property (N) is the energy (E) of the system, which has three forms; internal

energy (Eu), potential energy (E P.E) and the kinetic energy (E K.E). Thus;

N = E sys = Eu + EP.E. + Ek.E.

= mu + mgz +

And;

(𝜌𝑣 𝜕

𝜕𝑦 𝜌𝑣

𝑑𝑦

)𝑑𝑦𝑑𝑧

𝜌𝑤𝑑𝑦𝑑𝑥 𝑑𝑦

…………………………….(3.20)

Fig. (15)

(𝜌𝑢 𝜕

𝜕𝑥 𝜌𝑢

𝑑𝑥

)𝑑𝑦𝑑𝑧

𝑚

(𝜌𝑢 𝜕

𝜕𝑥 𝜌𝑢

𝑑𝑥

)𝑑𝑦𝑑𝑧

𝑚

(𝜌𝑤 𝜕

𝜕𝑧 𝜌𝑤

𝑑𝑧

)𝑑𝑦𝑑𝑥

𝑚

𝑚

𝜌𝑢𝑑𝑦𝑑𝑧

𝜌 𝑑𝑥𝑑𝑧

(𝜌𝑣 𝜕

𝜕𝑦 𝜌𝑣

𝑑𝑦

)𝑑𝑥𝑑𝑧

𝑚

(𝜌𝑤 𝜕

𝜕𝑧 𝜌𝑤

𝑑𝑧

)𝑑𝑦𝑑𝑥

𝑚

𝑑𝑥

𝑑𝑧

Page 65: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 65

……………………………………..(3.21)

Thus; equ.(3.13) becomes;

1st law of thermodynamics:

Q - W = dEsys ……………………………………… (3.22)

Where: (Q=Heat) and (W=Work). Hence;

……………(3.23)

Now, the work (W) has two components; shaft work (Ws) and flow

work ( ∫

); i.e.;

W = Ws + WF

= Ws+∫

= Ws+∫

+∫

Hence, equ.(3.23) becomes;

∫ ∫ (

+e) General E.E. …………(3.24)

For steady flow,(

∫ )

; thus;

∫ (

) …………………………….(3.25)

Using (3.21); and for one inlet an one outlet (

)

*(

) (

) + ………..(3.26)

Now;

Page 66: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 66

Heat per unit mass

( ) work per unit mass

Where hT = Turbine head (m)

hp = Pump head (m)

Substitute (3.27) in (3.26) gives;

q - (

) (

) …………………..(3.28)

Equ.(3.28) is the Steady State Steady Flow Energy Equation (S.S.S.F.E.E). In

differential from, it can be written as;

dq- d = d

+ du + gdz + d

=

dq- d =du+pd

…………………..(3.29)

From thermodynamics;

du+ pd =Tds …………………(3.30)

and;

Tds-dq=d(ghL) ……………..(3.31)

Where;

s=Entropy (J/kgK)

hL=Losses head (m)

Thus; equ.(3.29) becomes;

+ d(ghL)=0 ………….(3.32)

Integrate equ.(3.32) between sections (1) and (2) for incompressible fluids ( )

using equ.(3.27); it is obtained (after dividing by g);

(

) (

) ……….. (3.33)

………………………….(3.27)

Available Energy

at section (1) Energy

Added Available Energy

at section (2)

Energy

Subtracted

Energy

Lost

Page 67: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 67

Fig. (16)

Equation (3.33) in the S.S.S.F.E.E. for incompressible fluids. It is applied between

two sections (1) and (2) along, the fluid flow, see Fig.(16).

3.4.1 Bernoulli's Equation (B.E.)

It is a special from of the E.E (3.33) along a streamline without losses (hL=0)

and with no shaft work (hp=0,hT=0). Thus, B.E. will be;

B.E. …………………………(3.34)

B.E. is applied for steady frictionless flow of incompressible fluid along a stream line

Notes for Application of equations (3.33) and (3.34) (E.E &B.E.)

1- Available energy of the fluid has three forms;

Pressure (flow) energy per unit weight (m)

Kinetic energy per unit weight (m)

Potential energy per unit weight (m)

2- Each term of the E.E. and B.E. represents energy per unit weight (head h (m)).

3- The energy of the fluid can be represented by four forms;

a- Total energy E = p

(J)

b- Energy per unit weight h =

(m) (N. m/N)

c- Energy per unit volume

(N/m

2)

d- Energy per unit mass

(J/kg)

4- In equs. (3.33) and (3.34), section (1) is upstream and section (2) is downstream.

Page 68: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 68

5- (hp) in the E.E. represents the energy per unit weight added to the fluid by a pump,

compressor, fan, blower. (hT) represents the energy per unit weight subtracted from

the fluid by a turbine or windmill.

6- To calculate the power (P);

P =

Thus; P = gh =

7- (V) in the E.E. and B.E. is the average velocity at the section.

8- (hp) in the E.E represents the output power (OP) of the pump. To calculate the input

(shaft) power (IP);

……………………(3.36)

Pump efficieny

9- (hT) in the E.E. represents the Input Power (IP) to turbine. To calculate the output

power (OP);

=

……………………..(3.37)

Turbine efficiency

10- Kinetic Energy Correction Factor ( ):

The K.E. term (

) in the E.E. does not represent the average of the K.E.

across the section. Instead, we should calculate (

) across the section, where (u)

is the variable velocity across the section. To account for that, we should use (

) in

the E.E, where is the K.E correction factor, calculated from;

Hence;

=

∫( (

) ……..………….(3.38)

For laminar flow in pipe (

(

) ),

For turbulent flow in pipe

Page 69: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 69

3.5 Law of Conservation of Linear Momentum: Momentum Equation (M.E)

This law represents the application of the Newton's 2nd

law for a system. The

property (N) is the linear momentum of the System (mv); that is;

( ) ............…………………… (3.39)

The R.H.S. of this equation is obtained from the general control volume equation (3.13).

Thus, with;

N = (mv) linear momentum

=

Equ.(3.13) becomes;

( )

..................………….(3.40)

Substitute (3.40) in(3.39), the general momentum equation (M.E) is obtained;

∑ ( )

( ) ( )

Since the force (F) and the momentum ( ) are vector quantites, equ.(3.41) may be

written in three directions as;

∑ = ( )

( ) ( ) …………..(3.41a)

∑ = ( )

( ) ( ) …………..(3.41b)

∑ = ( )

( ) ( ) …………..(3.41c)

For steady flow,( ( )

), and the general M.E. reduces to ;

∑ ( ) ( ) M.E for steady flow ..............….. (3.42)

Also,

∑ =( ) ( ) …………..(3.42a)

∑ =( ) ( ) …………..(3.42b)

∑ =( ) ( ) …………..(3.42c)

For problems with one inlet and one outlet, ( ) Thus, equs.(3.41)

and (3.42) become;

............…….…...(3.41)

Page 70: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 70

∑ ( )

( ) …………..(3.43)

∑ ( ) …………….(3.44)

This can be written in three directions as;

∑ ( )

( ) ………….(3.43a)

∑ ( )

( ) ………….(3.43b)

∑ ( )

( ) ………….(3.43c)

And;

∑ = ( ) …………..(3.44a)

∑ = ( ) …………..(3.44b)

∑ = ( ) …………..(3.44b)

3.5.1 Applications of Momentum Equation

3.5.1.1 Fixed Vanes (Blades)

Fixed vanes (or blades) are usually used to deflect a jet of fluid to a certain

direction ( ), see Fig.(17).

The momentum equation is used to derive expressions for the two Forces (Fx) and

(Fy) required to hold the blade stationary. The following assumptions for the problem are

used;

1- Steady flow.

2- Frictionless flow.

3- Incompressible fluid.

4- Change in P.E. is neglected (Zin=Zout)

Fig. (17)

Page 71: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 71

5- Atmospheric pressure at inlet and outlet

Applying the B.E. between the inlet and outlet gives;

The momentum equations (3.44a) and (3.44b) will be applied;

∑ ( )

- ( ) ( ) n l n ne

∑ ( )

Fy= ( ) n l n ne

The resultant force (F) is calculated as;

F=√

with

3.5.1.2 Moving Vanes (Blades)

3.5.1.2.1 Single Moving Vane

The vane here is moving with a speed (u), and the fluid jet is approached with

velocity (V1). To make this problem similar to that of fixed vanes, we use the principle of

relative motion, that is, assuming the vane fixed and the fluid is approached with relative

velocity (V1-u), see Fig. (18)

Fig. (18)

Page 72: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 72

The M.E is used to find ( ) and ( ) required to obtain the desired motion (with

velocity u). The M.E.(3.44) is applied on the relative model, thus;

∑ ( ) ( )……………….(3.45)

With;

Thus, we can show that;

( ) ( ) ( ) …………….. (4.46)

Fy= ( ) sin …………………. (3.47)

Power Delivered by the vane =

………… (3.48)

K.E. remaining in the jet =

……………… (3.49)

3.5.1.2.2 Series of Moving Vanes

A series of vanes are fixed on a wheel, and thus a rotational motion is obtained.

Compared to the single moving vane, where part of the mass flow rate ( ) can reach the

moving vane, for a series of moving vanes the entire mass flow rate ( ) will be used,

thus, the M.E. will be;

∑ ( ) ( ) ……………..(3.50)

Where;

=

And, thus;

Fx= (1-cos ) ( )( ) ……………(3.51)

Fy= n ( ) n ……………(3.52)

Power delivered by the vanes= Fx=

........……..(3.53)

K.E. remaining in the jet=

......………..(3.54)

Page 73: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 73

Fig. (19)

Note:

1- The most important application for a series of moving vanes are the turbine wheels,

pumps, compressor, fans,

2- If the blade moves towards the jet, then:

Vr=V1+u

Power=

v2>v1

3- If (V1) and (u) are not in-live, (Vr) is found by adding them vectorially;

Vr=V1 u

3.5.1.3 Forces on Pipe Bends

The momentum equation is used to

calculate the forces (Fx) and (Fy) required

to hold the vertical pipe bend shown in

Fig.(19). Equs. (3.44a) and (3.44b) is

applied here;

∑ ( )

( ) ( )

∑ ( )

( ) ( )

Where Wb=Bend Weight

Wf=Fluid Weight= ( =bend volume)

Notes:

1- Before applying the M.E, the C.E. and E.E. are usually applied between sections(1)

and (2) to find the unknowns that are not given with the data, such as (V2,p2,…..).

2- If the plane of the bend is horizontal, then;

a- (z1=z2) and (z) will not be used in the E.E.

Page 74: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 74

Fig.(20)

b- (Fx & Fy) will be in the horizontal plane

c- (Wb & Wf) will not appear in the y-M.E

d- There will be a M.E. in the z-direction (equ.3.44c), with;

∑ [no flow in the z-direction]

3- If there is more than inlet or outlet (such as in Y-bend),

we must use equs.(3.42a,3-42b and 3-42c).

3.5.1.4 Theory of Propellers

Propellers are used to generate thrust against the drag exerted by the fluid on a body

moving through it. The thrust is generated by increasing the momentum of the fluid

passing through it, see Fig.(20).

Applying M.E., equ.(3.44a);

F= ( - )= ( - )= ( - )=( ) …………(3.55)

Where A=

Area of propeller

Thus; ( - ) ……………………(3.56)

Applying B.E. from 1 & from 3

Page 75: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 75

Fig. (21)

Since p1=p4, hence;

p3-p2=

(

) ……………………..(3.57)

Equating equations (3.56) and (3.57), and simplification yields;

…………………….(3.58)

Output Power OP=FV1= ( ) …………………….(3.59)

Input Power IP=

(

)…………………(3.60)

K.E remaining in the slip stream=

( )

……………(3.61)

IP=OP+K.E. remaining in slip stream

The theoretical mechanical efficiency ( ) is;

( )

(

)

……………….(3.62)

If , then;

……………………………..(3.63)

( ) is maximum when ( ) is minimum, which occurs when ( )is large i.e.,

accelerating larger Q to a smaller ( ) for a given ( )

3.5.1.5 Jet Propulsion

I- Jet Engines

The thrust of the jet engine (Fth) is generated

by expanding the gases produced from burning a

fuel with air in the combustion chamber, to a

higher velocity (v2<v1), see Fig.(21) Applying

M.E,equ.(3.42a) gives;

Fth =(

)

or; Fth= ( ) ………………….(3.64)

Where f =

fuel-air ratio

Z1=Z2

Z3=Z4

Page 76: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 76

Fig. (22)

Fig. (23)

II- Boats

The pump of the boat accelerates the jet

of water from ( ) to ( ), see Fig(22).

Applying M.E. gives;

F= ( ) …………………..(3.65)

3.5.1.6 Rocket Mechanics

The rocket motor carries its fuel and oxidizer with it, and so, there is no mass flow

enters the motor, only exit mass flow rate exists (gases produced by burring the fuel and

oxidizer at a rate of ), and hence producing the thrust of the rocket motor ( ) The

mass of the rocket is changing with time, therefore we

have to apply the general M.E (equ.3.41b), see Fig (23);

R = Air resistance

mR = Mass of rocket body

mf = Fuel mass

Rate of fuel buring

Vr= Exit gas velocity relative to rocket

V1= absolute velocity of the rocket

V= rocket velocity w.r.t. a reference moving with the rocket

V=0 but

Rocket acceleration

Total mass m = mR + mf = mR + ( )

=( mR + mf)-

=mi - …………………….(3.66)

Where;

Initial mass of the fuel

mi= Initial mass of the rocket

M.E.;

∑ ( )

( ) ( )

Page 77: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 77

Euler's Equation

1- Friction flow ………………(3.71)

2- Along a s.l.

Fig.(24)

-R-mg= ( )

( )

-

Thus;

( )

……………………………(3.67)

( )

…………….(3.68)

Where

Fth= thrust of the rocket ………………..(3.69)

3.5.2 Euler's Equation of Motion

This equation is applied for frictionless flow along a streamline. To derive this

equation, we will apply Newton's 2nd

law the fluid element shown in Fig.(24).

Since V=V(s,t), then;

a=

=

……….(3.70)

Thus;

pdA-(p+

) -

(

)

Simplification yields;

3.5.3 Bernoull's Equation

Euler's equation (3.71) for steady (

) incompressible fluid ( const.)

yields;

Integrating this equation;

𝜃

(p+∂

∂ ) A

𝑐𝑜𝑠𝜃 𝑑𝑧𝑑𝑠

Page 78: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 78

Fig.(25)

Or;

=

3.6 Some Applications of Continuity, Momentum and Energy Equations

3.6.1 Losses due to Sudden Expansion

The head loss due to sudden expansion (he) from a C.S.A. (A1) to a larger C.S.A

(A2) is found by applying the three continuity, momentum and energy equations. The loss

in energy occurs due to formation of a separated region after the sudden expansion, see

Fig.(25) This region is a low pressure

region accompanied by the formation of

vortices. The following assumptions are

made to analyze the problem;

1- Steady incompressible turbulent flow.

2- Uniform velocity over the cross –

sections.

3- Shear forces on the wall are negligible.

4- At the sudden expansion section (1'), the lateral acceleration of the fluid particles in

the eddy along the surface is small, and so, hydrostatic pressure variation occurs

across the section (p=p1).

C.E: A1V1=A2V2 …………………………(a)

E.E:

=

……………………… (b)

M.E: p1A2-p2A2= ( )

………………...(c)

Solution of equs. (a), (b) and (c) simultaneously for (he) gives;

he =( )

(

) …………………(3.73)

For circular pipes;

he =* (

) +

…………………(3.73a)

Bernoulli's Equation

1- Steady flow

2- Incompressible fluid …………..(3.72)

3- Frictionless flow

4- Along the same s.l.

Page 79: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 79

Fig.(26)

3.6.2 Hydraulic Jump

A rapidly flowing stream of liquid in an open channel suddenly changes to a

slowly flowing stream with a larger C.S.A. and a sudden rise in elevation of liquid

surface. This phenomenon is called"

hydraulic jump". It converts the K.E to P.E.

and losses or irreversibilities (rough surface

of the jump), see Fig.(26). The following

assumptions are used;

1- Steady incompressible flow.

2- Uniform velocity across the C.S.A. A1&A2.

3- Shear forces at the wall are negligible.

4- Hydrostatic pressure distribution across the sections (1) &(2).

The continuity, momentum and energy equations are applied to the problem to find the

head loss (hj) due to hydraulic jump, and the new elevation (y2).

C.E.: A1V1=A2V2

A1y1.1 =A2y2 .1 ………………..(a)

E.E:

=

y1+

y2

……………….(b)

M.E: ∑ ( )

F1 – F2

………………….(c)

From (a) and (c);

√(

)

…………………(3.74)

From (b);

( )

……………(3.75)

3.7 Law of Conservation of Angular Momentum: Moment of Momentum Equation

The property (N) of the system here is the moment of linear momentum (mrxv).

This law represents the application of the Newton's 2nd

law of motion for a system;

Page 80: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 80

Fig.(27)

( rx )

rxF=

( ) …………………..(3.76)

The R.H.S of this equation is obtained from the general control volume equation (3.13).

Thus; with;

rx

= rxv

Equ.(3.13) becomes;

( )

∫ ( )( )

……..(3.77)

Hence, equ. (3.76) becomes;

r x F =

∫ ( )( )

......……..(3.78)

Equ. (3.78) is the General Moment of Momentum Equation. The most important

application of this equation is for turbo machines, in which the normal (n) and tangential

(t) coordinates are used, see Fig.(27). The C.V. is the annular flow bounded by the root

circle (r1) and the tip circle (r2) of the blades.

The flow is assumed steady. The torque (T)

on the (C.V.) is produced from the tangential

components of forces (Ftr). Thus, with;

rxv=rVt

v.dA=VndA=Q=Q2=Q1

Equ.(3.78) reduces to;

Ftr=∫

=∫ ∫

Or;

T= ( ) ( ) Euler's Equation for Turbomachines ….(3.79)

For problems with more than one inlet and outlet, this equation becomes;

T=( ) ( ) .......................................…. (3.80)

Torque

on C.V.

Rate of Change of Moment

of Momentum in C.V. Net Efflux of Moment of

Momentum from C.V.

Page 81: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 81

Examples

Example (3.1): A two-dimensional reducing bend has a linear velocity profile at section

(1). The flow is uniform at sections (2) and (3). The fluid is incompressible and the flow

is steady. Find the magnitude of the uniform velocity at section (3).

Sol.:

C.E.:

0

0

*

+0

=1.35+0.45

∴ ⁄ ( -ve sign means inflow at 3 )

Example (3.2): Water enters a two-

dimensional channel of constant width

(h), with uniform velocity (U). The

channel makes ( ) bend that distorts

the flow to produce the velocity profile

shown at the exit. Evaluate the constant

(c) in terms of (U).

0

v = c ( 3.5 – x / h )

Page 82: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 82

Sol.:

C.E.: A1V1=A2V2

Uh1=∫

0 ∫ (

0)

Uh= *

+0

Uh=c*

+

Uh=3ch

∴ c=

m/s

Example (3.3): For the water tank shown in the

figure, calculate the exit velocity (V2) required to

lower the water level in the tank by (10 cm) in

(100 seconds).

Sol.:

Q1=A1V1=

( )

General C.E.:

( )

Thus;

( )

But;

0

00 m/s (level decreasing)

Thus; ( ) ( )

( )

=(0.00785+0.01) +0.001

( )

m3/s

0.7267=

( )

3

Page 83: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 83

Example (3.4): Neglecting the losses, calculate the required pump shat horsepower.

Sol.:

B.E. 1-2: 0+0+0=

+

…………….(1)

Man. Equ.: P2+0.6 +0.175*13.6 =0

0.6 – 0.175 * 13.6 = -2.98,

Sub. in (1) V2= 3.372 m/s

C.E.: A2V2=A3V3

V3= 23.98 m/s

E.E. 1-3: 0+0+0+hp= +( )

+0

∴hp=31.74 m

∴ kW =49.1 h.p.

Example (3.5): A horizontal axisymmetric jet of air ( kg/m3) with (10mm)

diameter strikes a stationary vertical disk of (200mm) diameter. The jet speed is (50 m/s)

at the nozzle exit. A manometer is connected to the center of the disk. Neglecting the

losses and the difference in potential head, calculate:

a- The deflection (h) of the manometer.

b- The force exerted by the jet on the disk.

c- The thickness (t) of the air jet at the exit.

Page 84: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 84

Sol.:

B.E. 1-2

( )

Man.equ.:

∴ cm =0.0888m

∑ ( )

-F=1.22*

( )

∴ n l

n

B.E. 1-3:

V1=V3

Qin= Qout

∴t=0.125 mm

Example (3.6): At what speed (u) should the vane shown in the figure travel for

maximum Power? What should be the angle ( ) for maximum power?

Sol.:

( )

-Fx= 0 ( cos - )

Thus;

Fx= 0 ( -cos )

or

Fx= 0( 0 ) ( -cos )

𝜌

Page 85: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 85

Power P=Fxu= 0( 0 ) ( -cos )

For maximum Power

0( -cos ) ( 0 ) ( 0 ) =0 u=

0

0[( 0 ) ( ) ]=0 =0 min. power

max.power

Example(3.7): An air plane traveling (400 km/h) through still air ( N/m3),

discharge (1000m3/s) through its two (2.25m) diameter propellers . Dertermine;

a- The theoretical efficiency b- the thrust c- The pressure difference across the propeller,

and d- The theoretical power required

Sol.

a- V1=400

000

00 m/s

V=

000

( )

m/s

b- F= ( )

( )

V=

Thus; F=

( )

c- F=( )

000

( )

=4.53 kpa

d- =

000

0 kW

Example (3.8): Determine the burring time for a rocket that initially has a gravity force

of (4.903 MN), of which (70 percent) is propellant. It consumes fuel at constant rate, and

its initial thrust is (10 percent) greater than its gravity force. The exhaust gases velocity is

(Vr=3300 m/s). Considering (g) as constant at (9.8 m/s2), and the flight to be vertical

without air resistance, find the speed of the rocket at burnout time, its height above the

ground, and the maximum height it will attain.

Sol.:

Page 86: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 86

Fth=1.1Wi=1.1*4.903 Fth=5.393 MN

Fth=

0

00 kg/s

Mass of propellant = 0 0

Hence;

The burring time=

= 0

buringtime=214.35 s

a=

( )

= 0 0

kg

Thus;

a=

00 00 0

00 0

Simplification gives;

Thus;

V ln( ) n

When t=0, V=0 ( )

Thus;

V ln(

0 )

at burnout, t=214.3, thus;

V ln(

0 )

The height at t= 214.3; (yb) is

yb=∫ ∫ * ln(

0 )+

0

0

y

The rocket will glide (V2/2g) higher after burnout, thus

ymax= yb+

=117.2*103+

y x

Page 87: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 87

Problems

The problems number listed in the table below refer to the problems in the

"textbook", chapter"3"

Article

No. Related problems

3.3 6,7,8,10,12,13

3.4

+

3.4.1

17,18,20,21,22,24,26,27,28,30,31,32,33,34,35,36,38,39,41,42,46

,47,51,52,53,54,55,58,59,60,61,63,64

3.5

+

3.5.1.3

70,76,77,78,82,84,85,87,88,89,125,137,138,139

3.5.1.1

+

3.5.1.2

100,111,112,113,114,116,118,120,121,122,123

3.5.1.4

+

3.5.1.5

91,92,93,95,97,99

3.5.1.6 101,102,105,106,107,108

3.6 127,128,130,133,134,136

3.7 140,141,142,143,144,145,146

Page 88: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 88

Chapter -4-

Dimensional Analysis and Similitude

4.1 Introduction

The solution of most engineering problems involving fluid mechanics rely on data

acquired by experimental means. The full-scale structure employed in the actual

engineering design is called the "PROTOTYPE", while the replica of the structure on

which tests are made is called the "MODEL", which is usually made much smaller than

the prototype for economic reasons.

The process of manufacturing the model, and the conversion of the experimental

results obtained from the model tests, both are based on laws and relations obtained from

“Dimensional Analysis” and “Similitude”, sees Fig. (1).

Fig. (1)

4.1.1 Dimensions and Units

"Dimensions" are physical variables that specify the behavior and the nature of a

certain system, whereas the "Units" are used to specify the amount of these dimensions.

In fluid mechanics problems, the "fundamental" dimensions are three; these are

Mass (M), Length (T) and Time (T). The dimensions of any physical variable include

these three dimensions (one, two or all). In heat transfer and thermodynamic problems, a

fourth dimension for temperature ( ) is added. Table (1) includes the dimensions of the

most important variables.

Prototype

Actual Full-

Scale Structure

Dimensional

Analysis &

Similitude

Model

Replica of the

Structure

Experimental

Results

Experiments

Page 89: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 89

Table (1)

Quantity Dimension Quantity Dimension

Mass M Dynamic Viscosity (μ) ML-1

T-1

Length L Kinematic Viscosity (ν) L2 T

-1

Time T Density ML-3

Force MLT-2

Pressure ML-1

T-2

Area L2 Specific Weight ML

-2 T

-2

Volume L3 Surface Tension MT

-2

Velocity LT-1

Power ML2 T

-3

Discharge L3T

-1 Work ML

2 T

-2

Angle M°L°T° Angular Velocity T-1

Notes:

1- Any analytically derived equation should be dimensionally homogeneous, i.e., the

sum of exponents for each dimension in the R. H.S. of the equation should be equal

to that in the L. H. S. of the equation. Also, the dimensions of each term in any

equation should be the same.

Examples:

1) Q = AV

L3T

-1 = L

2. LT

-1

L: 3 = 2 + 1 = 3

T: -1 = -1

2) P = γh

ML-1

T-2

= ML-2

T-2

.L

M: 1 = 1

L: -1 = -2 + 1 = -1

T: -2 = -2

Empirical equations need not be dimensionally homogeneous, for example, the

Chezy formula;

√ c = constant

Page 90: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 90

The equality of dimensions is absorbed in the constant of the equation (c).

2- In fluid mechanics problems, the maximum number of dimensions in any physical

quantity, or group of physical quantities is three dimensions (m=3), i. e., (m) could be

(0, 1, 2 or 3 (max)).

3- Physical variables in fluid mechanics are usually classified in to three groups;

1) Geometry Variables (L, d, A, V, Angle,)

2) Fluid Properties Variables ( , μ, ν, k, σ,)

3) Kinematics and Dynamic Aspects of Flow Variables (p, v, a, g, F, ω, P, W,)

4- Any variable which has no dimension is called "Dimensionless" variable; with

dimensions (M°L°T°).

4.2 Dimensional Analysis

The basic objective in dimensional analysis is to reduce the number of separate

variables involved in a problem to a smaller number of independent dimensionless groups

of variables called “Dimensionless Parameters”. As the functional relationship between

the variables can be analytically established (by using dimensional analysis), the

experimental work is reduced to finding the value of the constants. Dimensional analysis

can be gainfully used to plan the experiment and reduce the number of variables to be

tested; and the results can be presented meaningfully.

Consider, for example, the motion of a sphere in a fluid. The drag force (FD)

excreted by the fluid on the sphere is known to depend on the sphere diameter (D),

velocity (V), fluid density ( ) and viscosity (μ), see Fig. (2). If we want to study the

effect of the independent variable (P, M, V, D) on the dependent variable (FD), we have

to investigate the effect of each of the four variables, separately and keep the other three

constants. Thus, if, for example, we made (5) experiments for each variable, we need

(54 = 625) experiment to study these effects and relations, which is a very complex and

laborious process, since it involves the use of different fluids, different diameters and

different velocities. Besides; the results presentation is a very complex and cannot be

Page 91: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 91

representative. To solve this problem, we use the principle of dimensional analysis, by

which we replace the original relation;

( )………………. (4.1)

to the following relation:

(

)

Or ( )

We should note the following;

1- Number of variables in the original problem (equ. 4.1) is (n = 5).

2- Number of “dimensionless” variables in the transformed problem (equ. 4.2) is (2),

which is the difference between the number of variables in the problem (n = 5) and the

number of dimensions of the problem (m = 3).

3- The number of experiments in the original problem is (54 = 625), whereas in the

transformed problem it is (51 =5).

4- We note that ( , V, D) are repeated with (CD) and (Re) in (equ. 4.2). These are called

the repeated variables of the problem, and their number equals to the number of

dimensions of the problem (m = 3).

5- During the (5) experiments, we have to change (Re) five times and measure the drag

force (FD) and then draw the relation between them. The change of (Re) can be done

by changing one of the four independent variables ( , V, D, μ) and keep the other

three constants.

6- The obtained results (CD = f (Re) relation) can be used for different ranges of (P, V, D,

M) that used in the experiments.

7- The process of finding the dimensionless parameters (CD & Re) from the original

variables (FD, , V, D, μ) is made by using the “Buckingham - Theorem”, which

will be described in the next article.

4.2.1The Buckingham – Theorem

“If a physical phenomenon involves (n) quantities, and if these quantities involve

(m) dimensions, then the quantities can be arranged into (n-m) dimensionless parameter”.

..............................…………………….. (4.2)

CD = Drag Coefficient , Re = Reynolds Number

Page 92: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 92

Let (A1, A2… An) be the (n) quantities involved in the problem. A functional

relationship should exist such that;

( ) ……………………….. (4.3)

If the number of dimensions in the above (n) quantities is (m), then there exists (n-m)

dimensionless parameters called ( ) such that;

( ) ........…………… (4.4)

Where each ( ) term is a non-dimensional (dimensionless) product involving the above

quantities.

The method of determining the -parameters is to select (m) of the (A) quantities

with different dimensions that containing among them the (m) dimensions and use them

as “Repeating Variables” together with one of the other (A) quantities for each ( ). Thus;

The exponents are to be determined such that ( ) is dimensionless.

The Procedure for the Application of the -Theorem:

1- Select the (n) variables involved in the problem.

2- Write the functional relationship F (A1, A2… An) =0.

3- Identify the dependent variable of the problem.

4- Select the repeating variables;

a) They must contain the dimensions of the problem, collectively.

b) Each repeating variable must have different dimensions from the others.

c) They must be physically the most significant variables.

Ex.

d) They must not contain the dependent variable.

e) They must contain least dimensions (Ex. (v, g) choose v).

f) They should not form a - term by themselves.

………………….. (4.5)

(A1, A2, A3) are the repeating

variables

Page 93: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 93

g) It is essential that no one of the repeating variables be derivable from the others.

h) A variable of minor importance should not be selected as repeating variables.

5- Write the -parameters in terms of the unknown exponents;

6- For each -expression, writ the equations of the exponents so that the sum of the

exponents of each dimension will be zero.

7- Solve the equations simultaneously.

8- Substitute back into the - expressions of step (5- ).

9- Establish the functional relationship [f ( ) =0] or solve for one of the

( s ) explicitly; for example;

( )

10- Recombine, if desired to alter the forms of the - parameters, keeping the same

number of s [( ) (

) , c = constant].

4.2.2 Common Dimensionless Numbers

In a hypothetical fluid flow problem, the pressure difference ( ) between two

points in the flow field depends on the geometry of the flow

(l, l1, l2), fluid properties ( , μ, σ, K) and the kinematics of the flow (V and g). Thus;

F ( p, l, l1, l2, , μ, σ, K, V, g) = 0

n = 10

m = 3

Dependent Variable = p

Repeating Variables = , V, l

Or:

, which is called the ( Pressure Coefficient Cp )

No. of 𝜋 s = 10 – 3 = 7

Page 94: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 94

i.e.:

………………… (4.6)

× ×

×

(

)

Euler number (E) is usually defined as;

√ √

……………….. (4.7)

Or:

, which is called the ( Reynolds Number Re )

i.e.:

.....………………… (4.8)

Viscous Force

Thus; Re=

At high (Re), the effect of viscosity is small and the (Re) effect is negligible because the

intertie effect is large. High (Re) means either (v) is large or ( ) is small or (l) is large.

Or;

√ lle e ( )

i.e.;

y … (4.9)

Gravity Force Fg = weight =

Thus;

Page 95: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 95

( ) is used when there is density stratification, such as between salt water and fresh

water.

Or;

lle e ( )

i.e.;

… (4.10)

r e en n r e l

l

l l

Weber number (W) is used when surface tension effects are predominant, such as in

capillary tubes and capillary waves in channels.

Or;

√ lle ( )

i.e.;

..................… (4.11)

Where: C= speed of sound in fluid = √

Fc =

Mach number effects are important when (M > 0.3 or 0.4). (M) is a measure of the ratio

of K.E. of the flow to internal energy of the fluid.

… (4.12)

… (4.13)

are geometry parameters.

Hence;

Page 96: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 96

f (

)

Or;

(

) .....................................… (4.14)

Equation (4.14) includes all effects which could be involved in a certain fluid mechanics

problem. Usually, not all these effects exist with the same degree of importance, but one

of them (or two) usually overcome the other effects. The inertia effect, of course, exists

always in all applications, since it is responsible of the fluid flow. The pressure effect is

the dependent parameter of the problem.

4.3 Similitude

It is the theory and art of predicting the prototype performance from model tests

and observations. It involves the application of dimensionless numbers, such as (Re, Fr,

W, and M) to predicate prototype performance from model tests. The similitude involves

three types;

I- Geometrical Similitude

The shape of the model is similar to the prototype. The ratio between all

corresponding lengths (including roughness elements) between model (m) and prototype)

(p) are equal. The ratio ( ) is called the "Scale Ratio" or "Model Ratio". ( is read as

"lambda")

Length Ratio .........................… (4.15)

Area Ratio .........................…. (4.16)

Volume Ratio ........................… (4.17)

II- Kinematic Similitude

a- The paths of homologous moving particles are geometrically similar.

Pressure

Effect

Viscous

Effect Gravity

Effect

Surface

Tension

Effect

Compressibility

Effect

Geometry Effect

Page 97: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 97

b- The ratios of velocities and accelerations at homologous particles are equal.

Velocity Ratio

...............................… (4.18)

Acceleration Ratio

.......................… (4.19)

Discharge Ratio

..........................… (4.20)

III- Dynamic Similitude

This implies that in geometrically and kinematically similar systems at homologous

points the ratio of corresponding forces between the systems are same. This implies that

the dimensionless numbers derived in article (4.2.2) are the same between model (m) and

prototype (p);

(

)

(

)

Hence from equ. (4.14);

(

)

(

)

Or; (

) (

)

Hence;

.................................. (4.21)

Equ. (4.21) is a general formula. To find the force ratio between model and

prototype we need to calculate the velocity ratio ( ), which is found by equating (Re, Fr,

W, M) between (m) and (p). But since these numbers have different forms, each one give

different value for ( ), so, we cannot solve the problem by equating all these numbers.

Instead, we choose one of them which have greater effect than the others on the problem.

Most engineering applications for incompressible fluids, the (Re) and (Fr) are the most

important numbers. Each number has certain applications, as will be explained soon.

Page 98: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 98

4.3.1 Re - Criterion

This criterion is applied for engineering applications in which only inertia and

viscous effects are important. These include the following;

1- Flow in closed conduits (internal flow).

2- Flow around immersed bodies.

3- Flow in wind and water tunnels.

The problem here is solved by equating (Re); thus;

(

)

(

)

Or;

........................ (4.22)

Substitute (4.22) into (4.21) gives;

Or;

............................ (4.23)

It is clear from equ. (4.23) that when the same fluid is used for the model and prototype

( ) , the force ratio is ( ), i.e. ( ). this result is for problems

using Re-criterion only.

4.3.2 Fr - Criterion

This criterion is applied for engineering applications in which only inertia and

gravity effects are important. These include the following;

1- Open channel flow.

2- Dams and spillways.

3- Hydraulic jump.

4- Ships and boats (neglecting viscous effects).

Now;

Page 99: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 99

Frm = Frp

(

√ )

(

√ )

Or;

√ √ ............................................ (4.24)

Substitute (4.24) into (4.21) gives;

............................. (4.25)

4.4 Ships Models Tests

The ships are usually exposed to two components of drag. These are viscous

(frictional) drag (FDv), which is a (Re- criterion), and the ware drag (FDw), which is a (Fr-

criterion). Thus, the total drag (FDT) is:

And;

To find the velocity ratio ( ), we use equs. (4.22) and (4.24). Thus;

Re – Criterion:

Vm < Vp ( since < 1 )

Fr – Criterion: √ √ Vm > Vp

So, we cannot solve the problem by equating both (Re + Fr), since each number gives

different value. To solve the problem, we test the model according to (Fr- criterion) and

use equ. (4.24) for ( ), and calculate the viscous drag (FDv) from existing relations. The

ship model is tested in the laboratory and (FDTm) is measured, with the velocity calculated

………………………………….. (4.26)

Re-Criterion Fr-Criterion

Page 100: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 100

from equ. (4.24). The following procedure is used to calculate the total drag on the

prototype and the power required to drive it;

1- Make a model test according to Fr- criterion, equ. (4.24), and measure (FDTm) in the

laboratory.

2- Calculate (FDVm) from analytical or empirical relation.

3- Calculate FDWm = FDTm – FDVm.

4- Using Fr- criterion, equ. (4.25), calculate (FDWp), i.e., FDWp = FDWm

5- Calculate (FDVp) from analytical or empirical relations.

6- Calculate ( )

7- Calculate the required ( Shaft Power = / ηp ), where (ηp) is the propeller

efficiency.

Note:

1. All problems of ships models tests which consider the viscous (FDV) and gravity

(FDW) effects are solved by following the procedure described above (steps 1 – 7).

The simple difference is in the relation used to calculate (FDV), steps 2 and 5.

2. If we neglect the viscous effects (FDV) and consider the gravity effects (FDW) only,

then the problem is solved according to Fr – Criterion ( Article 4.3.2 ).

Page 101: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 101

Examples

Example (4.1): The drag force (FD) on a sphere moving in a fluid depends on the sphere

diameter (D) and velocity (V), and the fluid density (P) and viscosity (M). Find the

functional relationship for the drag force (FD).

Sol.

F (FD, V, D, , μ) = 0

n = 5

m = 3

Dependent variable = FD

Repeating variable = m = 3 = ( , V, D )

: x1

Vy1

Dz1

FD

: x2

Vy2

Dz2μ

: Mº Lº Tº = (ML-3

)x1

(LT-1

)y1

(L)z1

MLT-2

M: 0 = x1 + 1

L: 0 = -3 x1 +y1 +z1 + 1

T: 0 = -y1– 2

Thus;

= -1

V-2

D-2

FD =

= CD Drag Coefficient

: Mº Lº Tº = (ML-3

)x2

(LT-1

)y2

(L)z2

ML-1

T-1

M: 0 = x2 + 1

L: 0 = -3 x2 +y2 +z2- 1

T: 0 = -y1 – 1

Thus;

= -1

V-1

D-1μ =

MLT-2

LT

-1

L

ML-3

ML-1

T-1

No. of 𝜋 s = n-m = 5-3 = 2

Properties Geometry

Kinematics & Dynamic Aspects

x1 = -1

y1 = -2

z1 = -2

x2 = -1

y2 = -1

z2 = -1

Page 102: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 102

Or;

Reynolds Number

Thus;

f ( ) = 0 f (CD, Re) = 0

CD = f (Re) The function (f) is found from experiments

Example (4.2): A(1/5) scale model automobile is tested in a wind tunnel with the same

air properties as the prototype. The air velocity in the tunnel is (350 km/h), and the

measured model drag is (350 N). Determine the drag of the prototype automobile and the

power required to overcome this drag.

Sol.:

Use Re-criterion (equs. 4.22 and 44.23).

Rem = Rep

Equ. (4.22):

Since the same air is used ( ), thus;

Equ. (4.23):

Power = 000

00 er

Example (4.3): The wave resistance of a model of a ship at (1:25) scale is (7 N) at a

model speed of (1.5 m/s). What are the corresponding velocity and wave resistance of the

prototype ? Assume the model is tested in fresh water ( = 1000 kg/m3) and the ship will

operate in the ocean where (s = 1.03) for the water.

Sol.:

Use Fr-criterion (equs. 4.24 and 44.25).

Frm = Frp

Equ. (4.24): √ √ Vp = 1.5√ √ Vp = 7.5 m/s

Equ. (4.25): Fp = 7 * 1.03 * 1 * 25

3 Fp = 112656 N

Page 103: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 103

Example (4.4): A (10 m) model of an ocean tanker (500 m) long is dragged through

fresh water at (3 m/s) with a total measured resistance of (103 N). The surface drag

coefficient ( cf ) for model and prototype are (0.245) and (0.0147) respectively, in the

equation ( F = cf A V2 ). The wetted surface area of the model is (20 m

2). Find the total

drag on the tanker and the power required at the propeller shaft assuming an efficiency of

(90 %) for the propeller.

Sol.:

FDVm = cfm Am Vm2 = 0.245 * 20 * 3

2 FDVm = 44.1 N

FDWm = FDTm – FDVm = 103 – 44.1 FDWm = 58.9 N

Using Fr-criterion;

Vp = Vm√ √ = 3 √ √ Vp = 21.2 m/s

FDWp = FDWp FDWp = 58.9 * 1 * 1 * (500/10)

3 FDWp = 7362500 N

( 00

0) Ap = 20 * 50

2 Ap = 50000 m

2

FDVp = cfp Ap Vp2 = 0.0147 * 50000 * 21.2

2 FDVp = 330338.4 N

= 7692838.4 N

er er

Problems

The problems number listed in the table below refer to the problems in the

"textbook", Chapter "4”;

Article No. Related Problems

4.1 5,6

4.2 2,8,10,11,12,13,17,20

4.3 18,21,23,26,33,35

Page 104: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 104

Fig. (5.1)

Chapter -5-

Viscous Fluid Flow

5.1 Introduction

In viscous flow, the viscous (frictional) effects are very important and must be

considered. Real (viscous) fluid flow may be either laminar or turbulent. In laminar flow

(low Re) the influence of viscosity is predominant. In turbulent flow (high Re) the inertial

effects are predominant.

5.2 Equations of Motion for Viscous Flow

These equations must include

the following forces:

1. Pressure forces.

2. Inertia forces.

3. Viscous (shear) forces.

4. Body forces.

5. External forces.

For each plane:

(1) Normal stress ( ).

(2) Shear stresses ( ).

Thus;

6 surfaces 12 Shear forces

6 Normal forces

Also, there is; 3 Body forces ( ) per unit mass

3 External forces ( )) per unit mass

Hence; the total forces = 24 forces

Now; u=u (x, y, z, t), v = v (x, y, z, t) w = w (x, y, z, t)

( )

( )

( )

𝜏𝑥𝑦 𝜕𝜏𝑥𝑦

𝜕𝑥 𝑑𝑥

𝜍𝑥 𝜕𝜍𝑥𝜕𝑥

𝑑𝑥

𝜏𝑥𝑧 𝜕𝜏𝑥𝑧𝜕𝑥

𝑑𝑥

𝑑𝑥

𝑑𝑦

𝑑𝑧

𝜏𝑥𝑦

𝜏𝑥𝑧

𝜏𝑎𝑏

𝜍 a : axis normal to the plane

b : direction of stress

𝜍𝑥

Page 105: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 105

Stoke's law;

(

)

( )

(

)

( )

(

)

( )

(

) ( )

(

) ( )

(

) ( )

For incompressible fluids, the continuity equation reduces to;

( )

Now, the equations of motion for viscous flow are the Newton’s 2nd

law. Thus;

∑ x ∑ y ∑

z ( )

Applying (5.11) on the cubical element (Fig.(5.1)), and using the relations (5.1) to (5.10),

simplification and re-arranging yields the following equations of motion for viscous

incompressible fluids. They are known as “ Navier Stokes” equations;

(

) ( )

(

) ( )

(

) ( )

Local

Acclamation Convective Acceleration

Inertia forces

Pressure

Forces

Body

Forces

External

Forces Viscous forces

Page 106: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 106

5.3 Laminar Flow Between Parallel Plates: “Couette Flow”

Assumptions:

1. Steady incompressible flow (

)

2. One – dimensional flow (v=0, w=0) and (

)

3. Fully – developed flow (

( ) )

4. Newtonian fluid (

)

5. Parallel flow (

)

Applying the Newton’s law for the element of Fig.(5.2);

∑ ( ( ))

Thus;

(

) (

)

Using ( n = - dh/dx) and simplification yields;

( ) ……….....(5.15)

but;

(Newton's law of viscosity). Thus;

( ) …………...(5.16)

Integrate equ. (5.16) twice to obtain;

Fig. (5.2)

(𝑝 𝜕𝑝

𝜕𝑥 𝑑𝑥 )𝑑𝑦

(𝜏 𝜕𝜏

𝜕𝑦 𝑑𝑦 )𝑑𝑥

𝜏𝑑𝑥

n 𝜃 𝑑

𝑑𝑥

Page 107: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 107

( )

………...(5.17)

B.Cs. ; at y=0 u=0 →B=0

at y=a u=U →A=

( )

Thus; equ. (5.17) gives;

( )

( ) ………...(5.18)

The volume flow rate (Q) across the section is ;

0

( ) ………...(5.19)

The shear stress

( )

( ) ………..(5.20)

The term

( ) in the above equation is constant for each flow. It can be calculated

by one of the following two methods;

1.

( )

( ) ( )

( ) ( ) > ( )

2.

( )

n ( )

Note; There are many other cases for equ.(5.17) with different boundary conditions;

these are :

1. Fixed plates (U=0)

( )

( )

2. Lower plate moving.

3. Upper plate moves upward when the shaded areas are equal, then (Q=0)

y = a u = 0

y = 0 u = 0

𝜏

y = a u = 0

y = 0 u = U

y = a u = -U

y = 0 u = 0

Page 108: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 108

4. Both plates move in opposite directions.

5. Free surface flow

5.4 Losses in Laminar Flow

For steady laminar flow, the reduction in ( ) represents the work done on

fluid per unit volume. The work done is converted into irreversibilities (losses) by the

action of viscous shear. Thus, the net work done and the loss of potential energy

represents the losses per unit time due to irreversibilities.

Fig. (5.3): Work Done and Loss of P.E. for a Fluid Particle

Net Power = n ( )

Substitute for each term in equ. (5.21), simplifying and neglecting higher order terms and

dividing by the element volume, and using equ.(5.15), it is obtained;

(

)

………...... (5.22)

For flow between two fixed parallel plates;

(𝜏 𝜕𝜏

𝜕𝑦 𝑑𝑦

𝑧) (𝑢

𝜕𝑢

𝜕𝑦 𝑑𝑦

)𝑑𝑥

𝑢 (𝑝 𝜕𝑝

𝜕𝑥 𝑑𝑥

)𝑑𝑦

𝑢 (𝑝 𝜕𝑝

𝜕𝑥 𝑑𝑥

)𝑑𝑦

(𝜏 𝜕𝜏

𝜕𝑦 𝑑𝑦

) (𝑢

𝜕𝑢

𝜕𝑦 𝑑𝑦

)𝑑𝑥

𝐹 𝑉

𝐹 𝑉

𝐹 𝑉

𝐹 𝑉 𝑝 𝜏 𝑢 (x,y)

𝑑𝑦 𝑑𝑥𝑑𝑦

x

n𝜃 𝑑

𝑑𝑥

y = a u = U

y = 0 u = -v

y = a 𝑑𝑢

𝑑𝑦 𝜏 = 0

y = 0 𝑢

Page 109: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 109

( ) n

( )

Thus;

∫ (

)

[

( )]

0

( )

Hence;

( ) …….... (5.23)

The power done by the fluid between (1) and (2) is;

( )

( )

( )

Thus;

( ) . ……….(5.24)

For horizontal flow, ( )

….....(5.25)

Note:

Equations (5.24) and (5.25) can be derived using the energy equation from (1)to (2);

( )

Thus;

( )

( ) …………...…….... (5.24)

For horizontal flows;

( )

Thus;

………... (5.25)

Page 110: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 110

Fig. (5.4)

y=a-r

dy = -dr

5.5 Laminar Flow through Circular Tubes and Annuli

The same assumptions used in article (5.3) for flow between parallel plates are

used and applied here. The difference is that the y-axis is replaced by the r- axis.

∑ ( ( r ( ))

(

) (

( ) )

n

Thus;

( )

( ) ….………….. (5.26)

Integrate once;

( ) ………………... (5.27)

But;

Hence, (5.27) becomes;

( )

Integrate;

( )

( ) ……………... (5.28)

Equation (5.28) is applied for both circular tubes and annuli the difference is in the

boundary conditions.

𝜏 𝜋𝑟𝑑𝑥 𝜕

𝜕𝑟(𝜏 𝜋𝑟𝑑𝑥)𝑑𝑟

(𝑝 𝜕𝑝

𝜕𝑥𝑑𝑥) 𝜋𝑟𝑑𝑟 𝜏 𝜋𝑟𝑑𝑥

𝑝 𝜋𝑟𝑑𝑟

𝑑𝑤 𝜋𝑟𝑑𝑟𝑑𝑥

Page 111: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 111

5.5.1. Circular Tubes: Hagen - Poiseuille Equation

The boundary conditions for equation (5.28) are;

( )

Thus:

( ) ………………... (5.29)

The maximum velocity ( ) is at (r=0);

( ) ………………. (5.30)

The average velocity (V) is;

( )

0

Hence;

( )

………... (5.31)

Thus; equ. (5.29) can be written as ;

(

) (

) ………... (5.32)

Now, the volume flow rate (Q) is;

( )

0

... (5.33)

For horizontal tubes; h= constant;

( )

Hence

Hagen - Poiseuilli equation .... (5.34) (horizontal tubes)

Thus;

……………... (5.35)

And ; for horizontal tubes

………………... (5.36)

Page 112: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 112

The shear stress ( ) is calculated as ;

( ) ………...(5.37)

Notes:

1. The term

( ) is calculated as in article (5.3) for flow between parallel plates.

2. For flow through circular pipes and tubes;

Re < 2000 laminar flow.

2000 < Re< 4000 transition flow.

Re> 4000 turbulent flow.

3. Equations (5.29) and (5.32) are for fully - developed flow, for which (

), which

occurred far from the entrance of the pipe.

5.5.2 Annuli

The boundary conditions for equ.(5.28) are;

At r = a u = 0

r = b u = 0

Thus, we can show that;

( ) *

ln

+ ……….... (5.38)

( ) *

( )

+ ……….. (5.39)

𝜏𝑤

𝜏

𝜏

Page 113: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 113

5.6 Boundary –Layer Flow

Boundary –layer (b.l.) is a very thin layer of fluid adjacent to the surface, in which

the viscosity effects are important. The flow inside the boundary –layer is viscous (real)

flow, while outside the boundary-layer (main stream) the flow is inviscid (frictionless,

ideal).

u

S= b.l. thickness

Turbulent b.l.Transition

zone

Laminar

b.l.

Viscous flowSt

Frictionless (ideal, in viscid) flowU

Sy

U

x

Fig.(5.5): Growth of b.l. along a Smooth Flat Plate

To derive the equations of boundary –layer, we will apply the M.E to a control volume of

the b.l over a surface.

∑ =

( ) ( ) ( )

For steady flow of incompressible fluid along one side of a

smooth plate, the only force acting is due to drag or shear at

the plate, since the pressure is constant across the b.l. and

around the periphery of the c.v. of Fig.(5.6). Thus, for unit depth of the plate;

∑ ∫ ( ) ( ) ( ) …..(5.40)

C.S. ( )

AD

BC ∫

0

0

AB -∫

0 - ∫

0

Hence, equ.(5-40) gives;

Fig.(5.6)

Fx=∫ 𝜏𝑤𝑥

0𝑑𝑥

y

AU

B U

XCSkin – frictional dtag

x

Uu

y

Page 114: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 114

Fx=∫

0 ∫ ( )

0∫

0(

) …………. (5.41)

The velocity profile inside the b.l.(

)is usually given as;

(

) (

)=F( )

Where

&dy=

y=0

y=

Thus, equ.(5.41) becomes;

Fx=∫

0 ∫

0(

)

0

0

(

)

Hence;

0(

) ………………. (5.42)

Equation (5.42) is the M.E for 2-D steady flow along a flat plate (b.l. equation). The

problem of the b.l. is to find;

1. Boundary –layer thickness along the plate ( )

2. The skin-frictional force ( ∫

0 )

Equation (5-42) is a general equation applicable for both laminar and turbulent boundary

layers. The only difference is in the form of the velocity profile (

)

5.6.1 Laminar Boundary – Layer

The velocity profile inside the laminar b.l. is given by the following formula;

( )

0 =1 y> ………. (5.43)

(5.43) in (5.42) gives;

∫ (

)(

0

) =0.139

…….. (5.44)

At the wall;

0

0

(

)

Thus;

η

η

η

η

U

y U

uy

u

δ

U

u / U

1

ξ

ξ δ

y

1

u / U

1

ξ

ξ

y

δ

(5.43)

Page 115: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 115

…………. (5.45)

Equation (5.44) and (5.45) gives;

10.78

dx

Integrate with B.C (x=0, );

Substitute (5.46) into (5.45) gives;

……………………………….. (5.47)

The skin-frictional drag force ( ) is;

∫ √

0……………….. (5.48)

The skin-frictional drag coefficient ( ) is;

Note:

For Re<5* Laminar b.l.

5* < e < Transition

Re> Turbulent b.l.

5.6.2 Turbulent Boundary –Layer

The velocity profile is given by the 1/7th

power law;

(

) ⁄ = ⁄ ………………… (5.50)

(5.50) into (5.42) gives;

………………….. (5.51)

Equ.(5.50) cannot be used to find (

0) since it has no derivative at (y=0).

Therefore, an empirical formula for ( ) is used;

(

) ⁄ ………….. (5.52)

ere 𝑅𝑒𝑥 𝜌𝑢𝑥

𝜇

𝑢𝑥

𝑣………………………………… (5.46)

Where:

𝑅𝑒𝐿 𝜌𝑢𝐿

𝜇

𝑢𝐿

𝑣………………………………… (5.49)

Page 116: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 116

Equate (5.51) and (5.52), and integrate with B.C.(x=0, ), i.e., we assume turbulent

b.l. from (x=0); we get;

0

⁄ …………………….. (5.53)

From (5.52); (

) ⁄ ……………… (5.54)

And ∫

0 0

0…………. (5.55)

&

0 0

⁄ ……………………….. (5.56)

Note: If we take the laminar part of the b.l. into consideration; then:

0 0

00

…………………… (5.57)

Boundary-Layer Displacement Thickness ( )

It is the distance that the main stream (inviscid flow) is displaced due to the

existence of the boundary-layer;

∫ ( )

0 dy

Thus;

∫ (

)

0 dy

= ∫ (

)

0 ……………. (5.58)

5.6.3 Boundary-Layer Separation

The fluid inside the b.l. is affected by three forces;

1. The forward pull due to the momentum of the outer free moving main stream

(with velocity U).

2. The retarding viscous forces on the solid boundary (frictional effects).

3. The pressure forces due to pressure gradient along the boundary, which may be

either negative (or favourable

< ) or positive (adverse

> ) or zero

pressure gradient (

)

δ

L

t

x

Page 117: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 117

𝐹𝐷𝑝 𝑊𝑎𝑘𝑒

𝐹𝐷𝑓

𝐹𝐷𝑓 < 𝐹𝐷𝑝

Separation of the boundary –layer occurs when the resultant of the above three forces

become against the flow direction, and thus pushes the flow far away from the surface

and causes separation of the boundary-layer, see Fig.(5.7).

Notes:

1. Separation occurs when (

> ) only. When (

flat surfaces) or when

(

< ), no separation can occur.

2. The onset of separation is the point at which (

0 )

3. The region between the separation s.ℓ. and the boundary is called "wake" of the

body.

4. The "wake" of the body caused additional

"pressure or form drag" in addition to the

"skin-frictional drag"

FD = FD = Total Drag

5. In the design, we have to delay the separation point in order to reduce the wake size.

6. The separation point depends on;

a- The body shape.

𝜕𝑝

𝜕𝑥<

𝜕𝑝

𝜕𝑥>

𝜕𝑢

𝜕𝑦 𝑦 0

𝜕𝑢

𝜕𝑦 𝑦 0 >

𝜕𝑢

𝜕𝑦 𝑦 0 <

U

p pmin actual

Ideal

Fviscous Fpress Ffree stream

Separation s.l.

wakeu=0

Page 118: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 118

b- The roughness of the surface.

c- The turbulence level in the free steam.

d- The Reynolds number.

e- Flow conditions.

5.7 Drag and Lift

The drag force (FD) is the force component parallel to the

relative approach velocity excerted on the body by the moving fluid.

The lift force (FL) is the fluid force component on a body at right

angle to the relative approach velocity

FD= …………………………………. (5.59)

<

>

>

The drag coefficient (CD) is defined as;

CD=

…………………………. (5.60)

Where;

A=projected area perpendicular to the flow ( U), except for

airfoils, where A=c*s

Generally;

(Re,Shape)

= (M,Shape)for compressible flow

See Fig(5.21) and Table (5.1) in your textbook

The lift coefficient (CL) is defined as;

CL=

………………… (5.62)

See Fig.(5.23) & Table (5.1) in your textbook.

Total (profile)

Drag Skin (frictional) Drag

(viscous effects)

Pressure (form) drag (wake effect)

……….. (5.61)

U

FL

FD

U

FL

FDα

Disc

Stokes

law

sphere

CD

C= chordS= span

S

C

Re

CL

CD

22Angle of attack

α

Page 119: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 119

𝐷 𝑟

𝑈

𝐹𝐷

𝐹𝐵

𝑊

𝐅𝐢𝐠 (𝟓 𝟖)

Stoke's Law

The flow of viscous incompressible fluid around a sphere with very small Re

(Re=

< ) has been studied by Stoke. He found that;

FD=6 ………….. (5.63)

To find the terminal velocity (U) of the sphere (at which a=0),

see Fig.(5.8);

FD + FB = W

6

=

Thus;

U =

( ) …………………… (5.64)

To calculate the drag coefficient (CD) for this case;

CD =

Thus;

………………….. (5.65)

5.8 Resistance to Flow in Open and Closed Conduits

P

A

Z2ϴ

Z1

W

X

ɤAL

A=C.S.A.

P= wetted perimeter

sin ϴ= Z1 -Z2

L

Fig.(5.9): Uniform flow in Conduits

Page 120: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 120

Consider the steady uniform incompressible flow in conduit of constant C.S.A. (A)

and wetted perimeter (p), see. Fig.(5.9). We wish to calculate the head loss due to friction

hf between sections (1) and (2).

E.E. 1-2:

………………….. (5.66)

C.E.: A1V1=A2V2

Since A1=A2=A ………………. (5.67)

M.E.: ∑ [since =0 (steady and v=const.)]

Thus;

( )

…………….. (5.68)

The wall shear stress ( ) is usually defined as;

*

…………….. (5.69)

Where Fanning friction factor (found experimentally, or theoretically)

Using (5.66), (5.68) and (5.69), we can show that;

………………. (5.70)

Where

hydraulic radius

For circular pipe,

Equation (5.70) is a general relation applicable for open and closed conduits, laminar and

turbulent flow, and for any shape of uniform cross-section.

The head loss per unit weight per unit length ( ) is defined as;

S=

…………………. (5.71)

Thus;

V=√

√ √ …………. (5.72)

Where;

C = √ ⁄ ; Equation (5.72) is called Chezy formula.

Page 121: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 121

5.8.1 Open Channels Flow

For incompressible, steady flow at constant depth in prismatic (constant C.S.A)

open channels, "Manning" formula is widely used, in which;

C=

……………………….. (5.73)

From (5.72);

V=

⁄ ⁄ ……………………………… (5.74)

Where;

Cm=(1) in SI units and (1.49) in U.S units

S= slope of the bottom of the channel=slope of the water surface

n= Absolute roughness coefficient, depends on roughness of the surface (see Table (5.2)

in your text)

The discharge Q=Av=

⁄ ⁄ …………………….. (5.75)

Note: For open channel; (p1=p2), thus;

( )

S=

( )

slope of the channel

5.8.2 Steady Incompressible Flow through Pipes

For pipes,

…………………………. (5.76)

Where;

f=Darcy friction factor

Knowing that (

) equ.(5.70) becomes;

…………….. (5.77) Darcy-Weisbach equation

All quantities in equ.(5.77) except (f) can be measured experimentally. The Friction

factor (f) is known to depend on the following parameters;

f=f(V,D, ) ………………….(5.78)

Page 122: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 122

where;

measure of the size of the roughness projection (m)

measure of the arrangement or spacing of the roughing

m= from factor, depends on the shape of the individual roughness elements,

dimensionless

Since (f) is a dimensionless factor, it can be shown (using -theorem);

f=f (

,

,

,m)

=f (Re,

,

,m) ………………..(5.79)

The term (

) is called the "relative roughness". The experiments of Nikaradse show that

for one value of (

), the (f Re) curve is smoothly connected regardless of the actual

pipe diameters (D). The experiments proved that for one type of roughness, the following

relation is applied;

f=f(

)………..(5.80)

Equation (5.80) is plotted as "Moody Diagram", see Fig (5.10) and (5.32) in your

textbook

103

104

105

106

107

108

Re

0.00001

0.005

0.02

2 4

Laminar

zone zone

crit ical Transit ing Turbulent zone

Complete Turbulent zone

f ≠ f (Re)

f ≠ f (Re)

Steel

Costion

Concted

wood

Type of pipe__

__

__

__

E/D

Smooth pipe

Blains ration

0.1

f

0.02

0.08

0.07

0.06

0.05

Fig.(5.10): Moody Diagram

f = f(Re,

f = 0

𝑅𝑒 ⁄

Page 123: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 123

For laminar flow, equation (5.35) is;

………. (5.35)

But *

+

Thus; with (5.77);

……………….. (5.81)

Thus, for laminar flow, (f) is independent of ( )

For turbulent flow in smooth pipe, Blasius relation is usually used;

f=0

⁄ ……….. (5.82)

Equation (5.82) is valid up to (Re=100000).

5.8.3 Simple Pipe Problems

They are the problems in which the pipe friction (hf) is the only loss exist. In these

problems, the variables are usually 6 (Q, L, D, hf, v, ). Three of these six variables are

generally given or may be determined, these are (L, v, ). Thus, three variables remained.

Accordingly three types of problems exist, which may be solved by using;

1- Darcy-Weisbach equation 2.C.E. 3. Moody Diagram

Type "I": (L,v, Q, D), to find : hf

Procedure;

1. Calculate V=

2. Calculate Re=

3. Calculate

4. By using (Re,

), calculated (f) from Moody Diagram

5. Calculate hf =f

Type "II" Given:(L,v, , D), to find : Q

Procedure:

1. Assume f=f1

Page 124: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 124

2. Calculate (V1) from hf =

3. Calculate

4. Calculate

5. Using ( ,

) calculate new value (f2) from Moody Diagram.

6. Compare (f1) with (f2) and continue until convergence is attaint

7. Calculate Q=

Type"III" Given (L, ,Q) to find ( )

Procedure:

1. Assume f=f1

2. Calculate (D1) from =

3. Calculate

=

4. Calculate(

)

5. Using (

) calculate (f2) from Moody Diagram

6. Compare (f1) with (f2) until convergence

7. D=D1

Note: In place of Moody Diagram, the following explicit form of (f) may be used;

f =

* (

) (

0 +

Also, Colebrook formula may be used;

√ [(

) (

√ )]…………………(5.84)

Equation (5.84) is for commercial pipes in transtion zone

5.8.4 Secondary (Minor) Losses

They are the losses occurred in pipelines due to bends, elbows, joins, valves,…etc.

They are called secondary losses, while the frictional losses (hf) are called "primary

losses". Thus;

<

𝐷

5000 𝑅𝑒

………..(5.83)

Page 125: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 125

Total losses=Primary (Frictional) Losses +Secondary (Minor) Losses

= hf + hminor

=f

…………………. (5.85)

Where (K) is the loss factor for the minor losses. It is found experimentally, except losses

due to sudden expansion or contraction.

1. Loss due to sudden Expansion (he)

he=( )

* (

) +

……..(5.86)

Thus;

* (

) +

…………… (5.87)

If the expansion is form pipe to reservoir (

) , then

( ) and the complete kinetic energy (V2/2g) is converted

into thermal energy.

2. Losses due to sudden Contraction (hc)

The head loss due to sudden contraction (hc) may be

found using equ.(5.86). The proces of converting

pressure head to velocity head ((1) ( )) is very

efficient and hence the head loss from (1) to (0) is small

compared to the loss between (0) and (2). Thus;

hc= 0 0 ( 0 )

…………………(5.88)

C.E. 0 0=

or; 0 0

……… (5.89)

Where; Contraction Coefficient (found experimentally)

Thus;

=(

)

……………… (5.90)

And hence; (

)

0

V1V2

K= 1

0

V2P2

V1

D1

Vena contract

Page 126: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 126

3. Head loss at Pipe Entrance

K= 0.5▼

Square intel

K= 0.5

Round intel

K=0.01 – 0.05

Re-entrant intel

K=0.8 – 1

Note: see table (5.3) in your textbook for (k) values.

Equivalent Length (Le)

Minor losses may be expressed in terms of equivalents length (Le) of pipes that have the

same head loss for the same discharge thus;

k

………………….(5.88)

minor losses may be neglected when they are only (5%) or less than (hf). In general,

minor losses may be neglected when there is (1000D) length between each minor loss.

Note;

L L Le

V DD X V Q Q

Page 127: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 127

Examples

Example (5.1): The upper plate shown in the figure is moving to the right with (Vu=80

cm/s) and the lower plate is free to move laterally under the action of the viscous forces

applied to it. After steady –state conditions have been established, what velocity (Vℓ)

will the lower plate have? Take:(t1=2mm, t2=1mm, 0.1 Pa.s, 0.04 Pa.s).

Assume constant pressure for the two plates.

Sol.:

Since p= constant & , then:

u =

&

[

]

*

+

= 0.8*0

0

0 0

0

0

0

+

∴ cm/s

Example (5.2): In the piston-cylinder apparatus for pressure gage tester shown in the

figure, the piston is loaded to develop pressure of known magnitude. Calculate the mass

(M) required to produce (1.5 MPa(gage) in the cylinder, when

the piston moves with (0.02mm/s). Calculate also the leakage

flow rate of oil for these conditions. Assume steady uniform

flow and neglect the weight of the piston.

Sol.:

p*

er l e

Upper plate

Vu

V

t1

t2

Oil μ1

S1=0.9

Oli μ2 S2=0.9

τ1

τ2

S2=0.92

D

a

M

t1

Page 128: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 128

p*

………(1)

( )

[

]

=0 0 0 0

0 00 0

0 00 0

* 0

0 +

sub. In (1)

1.5*106*

( )

Q = (

*

+)

= (0 0 0 0 00 0

(0 00 0 )

0 )

∴ ⁄ ⁄ ⁄

Example (5.3): Determine the direction of flow through the tube shown in the figure, in

which ( = 8000N/m3) and ( Pa.s). Find the quantity flowing in liters per second

and calculate the Reynolds number for the flow.

Sol.:

Let the elevation datum be taken at section2;

p1+ h1=200000+8000*5=240 kPa

p2+ h2=300000+8000*0=300000 kPa

Since (p2+ h2)>( p1+ h1)

∴ Flow from (2) to (1)

( )

( ) ( )

( )

( )

( )

V=

=0 0000

(0 0 )

Re=

0 0 0 000

0 0

Since (Re<2000), the flow is laminar.

-ve

flow upward Q=-0.00036

𝑚

𝑠

=-0.0368L/s

1 p1 = 200 KPa

2 p2 = 300 KPa

10 mm ɸ

5m

Page 129: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 129

Example (5.4): For the hypothetical boundary –layer on the flat plate shown in the

figure, calculate:

a. The skin-frictional drag force on the top side per meter of width.

b. The drag coefficient of the top side.

c. The wall shear stress on the plate at the trailing edge.

d. The displacement thickness ( )of the boundary –layer at the trailing edge.

e. The displacement thickness ( )of the boundary –layer at the trailing edge.

Given constants: kg/m3 , =1.8*10

-5 Pa.s

3 mm4

3

1

2

U=40m/s

B.L.edge

L=30 cm

Sol.:

a- At section (3):

M.E.: -Fx=( ) ( ) ( )

C.S. ( )

12

34 ∫

0 ∫

0

23 - ∫

0 - ∫

0

- x ∫

+ ∫

Fx= ∫

=

0

0

=0.5

U

u

Page 130: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 130

= 0.1667 ( )

∴ 0.96 N on plate

b- CD

( )

∴ 0.00333

c-

0

0 0

0 00

∴ 0.24 Pa

d- ∫ (

)

0dy=∫ (

)

0

=*

+0

=

∴ 1.5 mm

Example (5.5): A smooth flat plate (3m) wide and (30m) long is towed through still

water at (20 c) with a speed of (6m/s). Determine the drag on one side of the plate and

the drag on the first (3m) of the plate.

Sol.:

For water at (20 c), from Table (c.1): ( = 998.2 kg/m3) and (v = 1.007 * 10

-6

). For

the whole plate;

× 0

00 × 0 Re = 1.787 *10

8 ; turbulent

0 0

0 = 0.0016

Drag force FD = CD *

PU

2 * L * b

= 0.0016 *

* 998.2 * 6

2 * 30 * 3 FD = 2587.3 N

Let (Retr = 5 * 105) at which transition to turbulent b.l. occurs;

Thus:

00 0 = 0.084 m

Page 131: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 131

For the first (3m);

00 0 Re = 1.787 * 10

7: turbulent

CD = 0 0

0 CD = 0.00255

FD = CD *

PU

2L * b

= 0.00255 *

* 998.2 * 6

2 3 * 3 FD = 412.7 N

Note: Ltr << L, so it can be neglected, and me assume the b.l. turbulent right from the

leading edge (x = O).

Example (5.6): How many (30m) diameter parachutes (CD = 1.2) should be used to drop

a bulldozer weighing (45kN) at a terminal speed of (10m/s) through still air at (100kPa)

and (20 C).

Sol.:

00000

( 0 ) = 1.19 kg/m

3

W = FD + FB

n = 0.4

n = 1 parachute

Example (5.7):A jet aircraft discharges solid particles of matter (d = 10 mm) and (s =

2.5) at the base of stratosphere at (11000m). Assume the viscosity ( ) of air to vary with

(y) from see level as ( = 1.78*10-5

-3.06*10-10

y). Estimate the time for these particles to

reach the see level. Neglect air currents and wind effects.

Sol.:

Using Stokes law;

( ); and assuming <<

Thus;

Thus;

Page 132: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 132

∫ ∫

0

000

0

( 0 ) 0 ∫ ( 0 )

0

000

Thus; t = 1301189 seconds = 15.06 day

Example (5.8): Determine the discharge for a trapezoidal channel (see the figure),with a

bottom width (b = 3m) and side slopes (1 on 1). The depth is (2m), and the slope of the

bottom is (0.0009). the channel has a finished concrete linins.

Sol:

From table (5.2) p.p. (230); text book, n = 0.012

×

A = 10 m

2

0

= 1.1547

Thus;

0 0 ( ) ( ) Q = 27.52 m

3/s

Example (5.9): Determine the head loss for flow of (140 L/s) of oil (v= 0.00001 m2/s)

through (400m) of (200mm) diameter cast iron pipe.

Sol:

0

0 0 0000 Re = 89127

From Moody diagram, Fig (5.32) p.p. 237 in your textbook, ( = 0.25mm)

Thus;

0

00

With (Re = 89127) and (

= 0.00125), from Moody diagram f = 0.023

= 0.023 * 00

(0 ) (0 )

= 46.58

Page 133: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 133

Example (5.01): Estimate the cost per month required to treat and circulate the water of

the swimming pool shown in the figure. The circulation rate is (0.1 m3/s) through

(100mm) diameter smooth pipe. The pump efficiency is (80%) and (1kwh = 65 fils).

Include all losses and also take (V = 10-6

m2/s).

Sol.:

0

(0 )

0

0

0

0

( 000)0

Apply the E.E. between two points on the free surface of the pool:

0 + 0 + 0 + hp = 0 + 0 + 0 + 0 + hℓ

hp = hℓ ∑

= [0.009407* 0

0 + 0.5 + 5 +10+10+20+10+20*0.9+10]*

( )

IP =

=

0 0

0

No. of kwh = IP * t = 874.29 * 30 * 24

∴ No. of kwh = 629488.8 kWh

Cost = 629488.8 * 0.065

∴ Cost = 40916.8 I.D.

Page 134: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 134

Example (5.00): The pump of the piping system shown in the figure is used to supply

(1m3/s) of water to the uphill station. Take (f = 0.014) and include all minor losses.

Calculate:

a. The required pump shaft power knowing that its efficiency is (80%).

b. The operational cost (in I.D.) of pumping (10000m3) of water to the upper reservoir,

knowing that: (1kwh = 300fils).

Sol.:

a-

∴ , = 7.96 m/s , = 14.15 m/s

∴ , ,

E. E.:

+

(

)

= ( )

( )

( )

+

( )

(

0 )

( )

0 0

0

Page 135: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 135

b-

0000

∴ t = 10000 s = 2.78 hr

No. of kwh = IP * t = 2600 * 2.78

∴ No. of kwh = 7228 kwh

7228 * 0.3

∴ Cost = 2168.4 I.D

Problems:

The problems number listed in the table below refer to the problems in the "text

book" , chapter "5".

Article No. Related Problems

5.3 1,2,3,6,7,9,10,11,12,13,14,16,17

5.5 20,21,22,24,27,28,29,31,33

5.6 43,44,45,46,47,48

5.7 42,49,51,52,54,55,56,57,62,63,64

5.8.1 65,66,68,69,70,72,75,77,78,81,82

5.8.2 +

5.8.3 +

5.8.4

25,83,84,87,88,89,90,95,96,98,99,

100,101,103,105,106,108,109,110,112,114,

115,116,117,118,119,120,121,123,124,125,129

Page 136: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 136

Chapter -6-

Fluid and Flow Measurements

The chapter includes the measurements method used for the most important fluid

and flow parameters, such as density, pressure, velocity, discharge, viscosity. All the

described methods involve the application of the basic fundamental principles covered in

the previous chapters.

6.1 Density Measurements

The most important methods are;

1. Weighing method; weighing a known volume ( )of the liquid;

=

………………. (6.1)

(w and ) measured

2. Buoyancy Principle: A solid object of known volume ( ) is weighed in air ( )

and in the liquid ( ) whose density ( ) is to be determined;

………………….. (6.2)

( ) measured

3. Hydrostatic Principle: Placing two immiscible liquids in a U-tub, one of known

density ( ), the other of unkown ( ).

……………… (6.3)

( ) measured

6.2 Pressure Measurements

At first, we must signify between three types of pressure. These are total

(stagnation) pressure (po), static pressure (p) and the dynamic pressure ( ). The relation

between these three types is;

po= p + pd = p +

……………….(6.4)

The static pressure (p) is the pressure of the fluid "sensed "or" feeled" by an observer that

is moving with the fluid with the same velocity (v) in magnitude and direction, i.e, the

Page 137: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 137

observer must not disturb the flow. The total (stagnation) pressure (po) is the pressure of

the fluid when it is stopped and comes at rest (v=0). If you swim in a river moving with a

velocity (V), and you leave your body to move "freely" without resisting the flow, then

the pressure you "sensed" or "feeled" is the static pressure of the flow. If you stopped

yourself in the river, then the flow becomes "stagnant" at your body (v=0), and hence the

pressure you "sensed" or "feeled" is the total (stagnation) pressure. The difference

between the two pressures is the dynamic pressure ( =

), which is a result of the

kinetic energy of the fluid.

Pressure measurements include the measurements of "static" and "total" pressure

only. The dynamic pressure is calculated as the difference between the two.

6.2.1 Static Pressure Measurements

The static pressure may be measured either by a "piezometer" opening or by a "static

tube"

V

Piezometer openings

V

Static holes

Static Tube

Piezometer Opening; a number of openings (holes) are made on the periphery of the

tube, pipe or duct. These holes are connected through a "ring" around them with one

opening connected to the manometer. When the inner surface of the tube is rough, this

method is not effective, since the flow will be disturbed. In this case, the static tube is

usually used.

V

Page 138: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 138

Static Tube; it is a blunt tube with closed nose and a number of

openings around the periphery at a section far away from the nose

(L>14d); to ensure that the flow becomes paralell after the nose

curvature.

Note: The discrepancy ( ) between the true and the measured static pressure normally

varies as the square of the velocity of flow, i.e. ;

………………….. (6.5)

Where (C) is a correction factor determined by calibration

6.2.2 Total (Stagnation) Pressure Measurements

This pressure is measured by using the "Pitot tube",

which is an open-nose tube. The flow at the open-end

comes at rest. This point is called "Stagnation Point", at

which (p=p0) and (V=0).

6.3 Velocity Measurements

The velocity is measured is measured through the measurement of the dynamic pressure

( =

) . As was mentioned earlier, this pressure is calculated as the difference

between the measured total (stagnation) and the static pressures. Thus;

= 0

0 √

0

…………………….. (6.6)

The "Pitot tube" and the " piezometer opening" or the static tube" are connected to the

same manometer to measure the velocity directly, as follows;

1. Combined Pitot Tube and Piezometer Openings

B.E. 1-2 =√

……………. (a)

Manometer equ.:

(

0

) ……………… (b)

Stagnation point (Po v=0)

L

d

Page 139: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 139

Thus;

√ ( 0

)………………… (6.7)

2. Pitot -Static Tube ; which combines the

"Pitot" and "static" tubes. The same relation

for the velocity (6.7) is applied here. A

correction factor (C) must be introduced into

equation (6.7) to take into account the losses

and errors. Thus, the actual velocity (Va) is

Va = C√ ( 0

) ………………… (6.8)

(C) is found by calibration

Note:

The " Pitot Tube" alone may be used to measure the velocity, as follows;

B.E. 1-2:

thus

but p2= ( )

p1=

Hence;

V=√

or ;

√ …………………. (6.9)

A correction factor (c) may also be used with this equation to calculate the actual

velocity;

Va = C Vt=C√

v

s

So

R

Page 140: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 140

6.4. Discharge Measurements

6.4.1 Orifice Meters

There are two types for this meter. One is used for reservoirs and the other for pipes.

6.4.1.1 Orifice in Reservoirs

B.E. 1-2:

Thus;

√ ………………….. (6.10)

The actual velocity ( ) is found by defining

the velocity coefficient ( ) as;

=

………………… (6.11)

Hence;

√ ……………. (6.12)

The actual discharge ( ) is given by;

………. (6.13)

Where;

A2= jet area at the vena-contract. (A2) is related to the orifice area (A0) through the

coefficient of contraction (Cc) by;

Cc =

0 ……………….. (6.14)

Thus; √ 0 0√

or;

0√ ……………….. (6.15)

Where;

……………… (6.16) discharge coefficient

…………….. (6.17)

Where; 0√ and

………………….(6.18)

Page 141: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 141

(Cd) may be found from equation (6.15) by measuring 0 H and ⁄ . Thus,

determination of either ( ) or ( ) permits the determination of the other from equation

(6.16). Several methods exists;

1. Trajectory Method; by measuring (x0,y0), the actual velocity ( ) can be determind

if the air resistance is neglected.

0 0

- 0

(

0

)

0

√ 0 ⁄ …… (6.19)

But √

Hence

2. Direct measurement of ( ) with a Pitot or Pitot –static tube placed at the vena-

contract (point 2)

3. Direct measurement of jet diameter by outside calipers

4. Momentum Method

∑ ( )

( )

But 0 × 0

Thus;

0

0………………….(6.20)

Losses in Orifice ; To calculate the losses in orifice, apply the E.E. between (1) and (2),

which gives;

(

)

(

)

Hence;

ℓ ( )

(

)……………….(6.21)

0

Page 142: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 142

Borda Mouthpiece

∑ x ( )

0

but; 0√

hence;

0 0√ √

Thus;

1=2 …………….. (6.22)

Unsteady Orific Flow from Reservoirs Time of Emptying Reservoirs

The determination of the time to lower the reservoir surface a given distance is an

unsteady flow case of some practical interest. If the reservoir Surface drops slowly

enough, the error from using B.E. is negligible.

C.E.

Thus;

or;

but

0√

hence;

0√

√ 0

Where (AR) is a known function of (y). If (AR= constant), then

0√ (√ √ ) ………………. (6.23)

0

Page 143: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 143

6.4.1.2 Orifice in Pipes

It is used to measure the discharge in pipes at law Re (low velocities). It is simply a

plate with central hole (orifice). To calculate the discharge (Qa);

B.E. 1-2:

………… (1)

C.E. A1V1=A2V2=Cc A0 V2

0 ……………. (2)

(1) and (2) gives;

(

0

) ………………….. (3)

Manometer Equation gives;

(

0

) ………….. (4)

Thus;

√ (

0 )

(

0

) ………………… (5)

And;

√ (

0 )

(

0

) ………………… (6)

The actual discharge (Qa) is;

Qa = 0 0 0

Hence;

Qa = 0√ (

0 )

(

0

) …………………… (6.24)

Note;

The orifice in a pipe causes vortices to be formed behind the orifice plate. These

vortices represent losses. The losses increase as the velocity increases. Therefore the

orifice in a pipe is used for low Re. At higher Re, Venturi meter is used.

Page 144: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 144

6.4.2 Venturi Meter

It is used to measure the discharge in pipes at high

velocity (high Re). The contraction coefficient is unity,

thus;

Cc=1

………………… (6.25)

B.E. 1-2:

…………….. (1)

C.E.

…………… (2)

(1) and (2) gives;

√ *

+

(

) ……………….. (3)

Manometer equ.:

(

0

) …………… (4)

Thus;

√ (

0 )

(

) …………………….(5)

Thus;

√ (

0 )

* (

) + …………………….. (6.26)

Thus; ( ) depends on ( ) regardless of the orientation of the venturi meter, whether it

is horizontal, vertical or inclined.

In the venture meter, no vortices is formed and the losses in energy is reduced, therefore

it can be used for high velocities.

S0

R-

K

h

1

Page 145: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 145

6.4.3 Rotameter

This device is used to measure the flow rate based on the princi ple that the drag force on

a body depends on the velocity over it. A "notched bob" is placed in a conical container

through which theflow passes over the bob. Applying force balance on the bob;

FD+FB=W

…………………… (1)

Where;

=Drag Coefficient

=Mean velocity in the annular space

Fluid density

Body density

Bob volume

Thus; Bob frontal area =

=√

(

) ………………… (6.27)

and;

Q=A √

(

) …………………. (6.28)

Where;

A=

( ) ……………………. (6.29)

A=Annular area

a= constant indicating the tube taper=2y tan

6.5 Viscosity Measurements

6.5.1 Rotating Concentric Cylinders

This method is based on Newton's law of viscosity;

Flow

w

Vm Vm

dFD FB

ƿ

y

D

ϴ

y

L

motor w

a

b

μ

dissStrings pointer

Torque

measurement

r1

r2

Page 146: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 146

When the outer cylinder is rotated, the motion is transmitted to the inner cylinder by the

action of viscosity ( ) of the fluid, thus excerting a torque (T) on it. This torque (T) is

measured by measuring the deflection angle ( ) rotated by the inner cylinder,

T=K …………………… (6.30)

Where K= stringe constant (N.m/deg)

This torque (T) equals the sum of the torques excerted on the cylinder walls (Tc) and

bottom (Td). Hence

T=Tc+Td

K =

∫ ∫

0

0

Or

K = *

+ ……………………… (6.31)

Thus, to measure the viscosity ( ), we need only to measure the deflection angle ( ),all

other parameters are known (specification of the device)

6.5.2 Capillary Flow Method

This method is based on the application of the Hagen-Poiseullif equation (5.34) for

steady, laminar incompressible flow.

Q=

…………………….. (6.32)

Q= ⁄

(Q,H) measured

( ) known

Thus, from equation (6.32), viscosity ( ) is measured.

6.5.3 Saybolt Viscometer

This method is also based on capillary flow and Hagen-

Poiseuille equation. It is used to measure the kinematic

viscosity ( ). The time (t) necessary to drain ( ml)

is recorded. (t) in seconds is the saybolt reading.

h

=60 m

Capillary tube

Diameter = D

Length = L

Const bath

temp.

Page 147: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 147

Q=

But Q=

and

Thus;

………………..(6.33)

Where h=head in the reservoirA correction term is added to equ.(6.33) totake into

consideration that the flow is not fully developed. Thus;

………..(6.34) (C1,C2)= constants of the device

𝑣𝜌

𝚤

Page 148: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 148

Examples

Example(6.1): A (75mm) diameter orifice under a haed of (4.88 m) discharges (907.6

kg) of water in (32.6s). The trajectory was determined by measuring (X0=4.76m) for a

drop of (1.22 m).Determine Cv,Cc,Cd, the head loss per unit gravity force, and the power

loss.

Sol.:

√ =√ m/s

t=√ 0 √

t=0.499s

0

0 m/s

0 000⁄

m

3/s

0 0√

( )

The head loss=H(1- ) =4.88(1- ) loss=0.241

Power loss= Q* Loss =9810*0.0278*0.241 Power loss=65.7 W

Example (6.2): A tank has a horizontal C.S.A. of (2m2) at the elevation of the orifice,

and the area varies linearly with elevation so

that it is (1m2) at a horizontal cross-section

(3m) above the orifice. For a (100mm)

diameter orifice, (cd=0.65), compute the

time, in seconds, to lower the surface from

2.5 to 1 m above the orifce.

Sol.:

Page 149: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 149

A=a+by

Thus;

A=2

y………………………(1)

C.E:

0√ =0

Hence;

t=

0√ ∫ ⁄

Using equ.(1);

t=

0

(0 ) √

∫ (

) ⁄

Which gives; t =73.8 s

Example (6.3): In the figure shown air is flowing, for which (p=101 kpa and T=5 °C)

and mercury is in the monometer. For (R'=200 mm), calculate the velocity (V)

Sol.:

V=√ ( 0

)

0 000

kg/m

3

0

0

Thus; V=√ ( ) V=205 m/s

a=2

b=-

0

Page 150: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 150

Problems

The problem number listed in the table below refer to the problems in the "text

book", (chapter(8)).

Article No. Related Problems

6.2 1, 2

6.3 3, 4, 5, 6, 8, 10

6.4.1 16, 18, 19, 20, 21, 22,23,24, 25,26, 27, 28, 29, 30, 31, 32, 34, 35, 36,

37, 38

6.4.2 39, 40, 41, 42

6.5 58, 59, 60

Page 151: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 151

Chapter -7-

Closed Conduits Flow Networks

7.1 Introduction

The analysis in this chapter is limited to incompressible fluid ( constant), i.e.,

liquids and gases with very small velocities. Isothermal conditions is assumed to

eliminate thermodynamic effects.

The network considered here consists mainly from (pipes, pumps, fittings, valves,

reservoirs). The analysis will be based on the fundamental principles and equations of

chapter "3" (Continuity and energy equations) and chapter"5" (viscous flow through

pipes, and calculation of the losses for the flow).

7.2 Pipe Friction Formula

In the network analysis, we need a formula that relates the head loss (hf) to the

discharge (Q) of the flow. (hf) here represents the frictional losses if we neglect the minor

losses, and it represents the total losses (frictional +minor) if the minor losses is to be

considered, in this case the length used represents the actual pipe length plus the

equivalent length (Le) for the minor losses. We will list here some of the conventional

formula used for this purpose;

Exponential Pipe –Friction Formula

………………………………. (7.1)

Where;

Head loss per unit length of the pipe

Q = discharge (m3/s)

D = inside diameter (m)

n, m ,R= constants

Hazen-Williams Formula

R = 0

n = 1.852 ; m = 4.8704

C= constant depends on pipe roughness

(........................... 7.2)

Page 152: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 152

Darcy- Weisbach Equation

=f

…………………… (7.3)

Equations (7.2) and (7.3) gives;

f = 0

0 0 e 0 ……………………….(7.4)

Conventional Formula

r ……………………………… (7.5)

r=constant depends on pipe

n= exponent (usually 2)

7.3 Concept of Hydraulic and Energy Grade Lines

The Hydraulic Grade Line (HGL) is a line showing the sum of pressure and

potential energies per unit weight (

z), while the energy grade line (EGL) represents

the total energy of the fluid (pressure, potential and kinetic energies per unit weight).

Both lines sloping downward with flow direction due to the losses in energy, except

across a pump, where the energy increases by (hp). Thus;

HGL =

z ………………………………… (7.6)

EGL =

z

…………………….. (7.7)

Hydraulic Gradient =

x(

z) …………………………… (7.8)

Energy Gradient =

x(

z

) …………………. (7.9)

Fig. (7.1)

𝑉

𝑔

𝑉 𝑔

𝑝

Page 153: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 153

Notes:

1. EGL is positioned (v2/2g) above HGL. Thus, if (v=0), as in a large reservoir, they

coincide.

2. Due to losses, EGL always slopes downward in the direction of the flow. The only

exception is when there is a pump:

Fig. (7.2)

3. If there is a turbine, there will be abrupt drop in EGL and HGL. The kinetic energy

can be converted to pressure energy by gradual expansion

If the outlet to a reservoir is an abrupt expansion, all the k.E. is lost, i.e., E.G.L. drops an

amount

at the outlet. If the flow passage changes in diameter, then the slope and the

distance between the EGL and HGL changes.

>

<

Fig. (7.4)

Fig. (7.3)

𝑝

Page 154: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 154

4. For negative (

), such as in a siphon;

Fig. (7.5)

5. For long pipes,(

) is small compared to (

) and may be neglected. Thus, the

EGL and HGL coincides.

Fig. (7.6)

7.4 Combination of Pipes

7.4.1 Pipes in Series

=……….=

ℓ ∑

………………… (7.10)

E.E.A-B Fig. (7.7)

H=

( )

(

)

Equivalent Pipes

Two pipes systems are said to be equivalent when the same head loss produce the

same discharge in both systems: Thus; for the two pipes to be equivalent;

𝑝

𝑝

Є1 Є2 Є3

Page 155: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 155

Fig. (7.8)

and

Hence;

And;

(

) …………………… (7.11)

Ex.: (D2=250 mm,L2=300 m, f2=0.018) and ( , =0.02). We want to find the

equivalent length of pipe (2) in terms of pipe (1). Using (7.11);

(

)

Thus; a (25.9 m) of (150 mm) pipe is equivalent to (300 m) of (250 mm) pipe for the

assumed conditions.

7.4.2 Pipes in Parallel

Q = Q1 + Q2 + Q3 +…….+ Qn

=(

z ) (

z )

Two types of problems exist;

Type (I)

Given (PA,ZA, PB, ZB), to find Q?

Procedure:

1. (

z ) (

z )=

2. Using the simple pipe problems method, with known, we can find (Q1,Q2,Q3)

from ( ) by using the relations in article (7.2) [hf ]

3. Using C.E.; Q = Q1 + Q2 + Q3

Type (II)

Given (Q) and (D, for each pipe), to find (Q1, Q2, Q3 and , , )

Procedure

1. Assume a discharge ( ) through pipe (1).

2. Calculate ( ) using (

).

............... (7.12)

Page 156: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 156

Fig. (7.9)

3. Using (

) calculate ( ) and (

).

4. Check C.E., If (

) is equal to the given (Q), then the solution is

over. If not,assume;

You can use ( ) and repeat steps (2-4) to check.

5. Calculate ( , , )from (

) and check that ( , , )

6. Q1= Q2=

Q3=

7.4.3 Branching Pipes

The following principles have to be applied in solving any

problem involving branching pipes;

1. A the junction (J), C.E. must be satisfied, i.e;

Inflow=Outflow

2. The Darcy-Weisbach or any pipe friction formula

should be satisfied for each pipe.

3. There can be only one value of piezometric head (

z) at any point including the

junction (j).

4. The flow will occur in the direction of falling piezometric head in a uniform pipe

length [(

z) (

z) ]

Three types of problems exist for this type of flow. (D, and Pipe friction

formula) are given.

Type "I"

Given Z1, Z2, Z3, Q1 Find Q2,Q3

Procedure:

1. Apply E.E. 1-J: (

) (

z)

+ .Here we assume that point (1)

is at the pipe (1) inlet, and we neglect the head of water in the tank; i.e.; and

( ) Thus; (

z) (assumed)

3 25 20 (assumed)

d

Flow

③ Z2

Z1

Z3

J

Page 157: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 157

Fig. (7.10)

2. Since (

z) > then flow is from J ( ) ( )

3. E.E. J (

z)

4. E.E J (

z)

Or; C.E at J: =

Type "II" Given Find:

Type "III" Given Find:

The last two types of problems are solved by trial and error since (

z) cannot be

calculated directly.

Procedure:

1. Assume (

z) ( ) The assumed value could be either larger than z (flow

from(1) (2)&(3)) or smaller than but larger than (flow (1) flow (2) (3))

2. Apply E.E.1 ( )

3. Apply E.E. J (or 2-J) =( )

4. Apply E.E J ( )

5. Check C.E at the Junction (J).If ( ), then the solution is over. If not

assume another value of (

z) and repeat the procedure from step (2) until

convergence, the new assume value should satisfy;

If ( > ) . Then assume higher value for (

z) .

If( < ) then assume lower value for (

z)

7.4.4 Pipe Networks

The flow in any network must satisfy the following

three basic conditions;

1. At each junction, the C.E. must be satisfied, i.e.:

Inflow = Out flow

2. The flow in each pipe must satisfy the pipe friction law

AB

C

D

E F

G

Page 158: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 158

Fig.(7.11)

for flow in a single pipe.

3. The algebraic sum of the head loss around any closed loop must be zero (because we

return to the same point).

“Hardy Cross Method” for pipe network is a systematic method for computation. It

consists from the following steps;

1. Assume the most suitable distribution of flow that satisfy the C.E.

2. Compute ( ) for each pipe ( +ve clockwise and -ve counterclockwise).

3. Check condition (3) i.e., ∑ ∑ for each loop.

4. If condition (3) is not satisfied, adjust the flow in each pipe by an amount ( ) for

each loop, i.e.;

and ∑

∑| 0 |

∑|

0| ………………… (7.13)

The numerator in equ. (7.13) is summed algebraically, while the denominator is

summed arithmetically. Hence, if ( ) it must be subtracted from clockwise

(Qo) and added to counterclockwise ones, and vice versa.

5. The above procedcare is repeated until ( ).

7.5: Pumping Stations

7.5.1: Single Pump in Pipe Line

Consider the single pump in the pipe line system

shown in the figure. The pump must fulfill the following

requirements;

1. Raise the fluid to a static Head (H).

2. Maintaine the flow rate (Q).

3. Overcome the losses in the pipe system.

4. Produce the k. E. with (V2) at the pipe exit.

To calculate the pump head (hp) required for these condition, apply the E. E. from (1-2),

which gives;

(

∑ )

Page 159: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 159

(7.12)

Fig. (7.13)

or; by using (V=Q/A), we can show that:

………………. (7.14) “System Curve”

Equ. (7.14) is called the “System Curve” , which gives the head (hp) that must be

supplied to maintain the flow.

To select a pump that fulfills the system requirement equ. (7.14), we have to know

the “pump characteristics”. For each pump, there is a “Pump Characteristics Curves” that

gives the relation between the pump head (hp), pump efficiency ( p or ep) and. The

discharge (Q), i. e. , two curves (hp Q and p ). These characteristics are usually

given in one of the following three forms;

1. Graphs:

2. Tables:

3. Equations:

………………. (7.15)

……………... (7.16)

where (a, b, c, d) are constants (could be + ve or – ve )

Now, if we select a pump whose characteristics are

given (either by curves, tables or equations) and placed it in

the system of Fig. (7.11), the point of intersection of the

system curve (7.14) and the (hp Q) curve of the pump is

called the “Operation Point”.

The designer always try to make the operation point

H

hp

Operation

point

Pump

character

ƺp

ƺp

System

curve

(7.14)

QQop

hp

Page 160: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 160

Fig. (7.15)

close the point of maximum efficiency.

If the pump characteristics equations (7.15 & 7.16) are used, equs. (7.14) and

(7.15) are solved simultaneously to obtain (Qop), i. e:

Qop = ( )

and then equ. (7.16) is used to obtain ( ).

The table may also be used by assuming a certain value of (Q), calculate (hp) from equ.

(7.14) and compare it with (hp) from table until

convergence.

If there is no point of intersection between the

system curve and the pump characteristics (H > static

head of pump), then either we select other pump with the

larger static head > H), or we can use the principle of

combination of pumps (similar or dis -similar ones).

7.5.2 Pumps in Series

For two (or n) pumps connected in series which is used to obtain "High Head " and "Low

Discharge"; see Fig. (7.15);

Q1= Q2 = --- =Qn =Qe ………….. (7.17)

hpe =hp1 +hp2+---+hpn ……….. (7.18)

Ipe= Ip1+Ip2

=

+

Thus,

pe =

----- (7.19)

If twin (2), or (n) "identical" pumps are connected in series, then

Q1 = Q2 = ---- = Qn (identical pump)…….. (7.20)

hp1 = hp2 = -- = hpn

Thus; from equs. (7.17) to (7.19); Fig. (7.16)

Fig. (7.14)

Page 161: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 161

Fig. (7.17)

Qe = Q1 = Q2 = --- = Qn ………(7.21)

hpe = nhp1 = nhp2 = --- = nphn ………(7.22)

pe = .…….(7.23)

7.5.3 Pumps in Parallel

This connection is used to produce "High Discharge" and "low Head". For two pumps

connected in parallel;

Qe = Q1 + Q2 + --- + Qn ……………(7.24)

hpe = hp1 = hp2 = --- = hpn ……………..(7.25)

IPe = IP1 + IP2

=

+

Thus;

pe =

……………. (7.26)

If twin (2) or (n) identical pumps are connected in parallel, then;

Q1 = Q2 = ---- = Qn

(identical pumps) ………… (7.27)

hp1 = hp2 = -- = hpn

Thus; from equs. (7.24) to (7.26);

Qe = nQ1 = nQ2 = --- = nQn …..…….(7.28)

hpe = hp1 = hp2 = --- = hpn ……………..(7.29)

pe = ……….(7. 30)

Note; "High discharge" is required when we want to reduce the time of operation of a

certain flow system (Ex. Filling a tank).

Fig. (7.18)

Page 162: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 162

Summary of Pumps Connections

If the pump characteristics are given by table or equation form, then the following table

summarizes the rules of connecting (n) identical pumps.

Connection Equation Table

Single Pump hp = a+bQ

2

= cQ+dQ2

hp Q

-

Increase

max ____

Decrease

-

-

-

Decrease

-

-

-

Increase

(n)Identical

Pumps

Connected In

series

hpe =n(a+bQ2)

= CQe+dQe2

Same

Value

Multiply

Each

Value

by(n)

Same

Value

(n) Identical

Pumps

Connected in

Parallel

hpe=a+b (

)

2

ƺpe= c (

) +d (

)

2

Same

Value

Same

Value

Multiply

Each

Value

by(n)

7.6 Conduits with Non-Circular Cross- Section

For ducts with non-circular cross -sections, the diameter (D) is replaced with

(Dh=4Rh), where);

Dh = Hydraulic Diameter =4 Rh =4

Rh = Hydraulic Radius =

…………… (7.31)

Thus;

hf = f

…………..(7.32)

Re =

…………… (7.33)

……………(7.34) (in Moody Diagram)

Page 163: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 163

EX:

1. Circular pipe =4

=4

=D

2. Square Duct =4

=a

3. Rectangular Duct =4

( ) =2

Examples

Example (7.1): determine the elevation of hydraulic and energy grade lines at points A,

B, C, D, and E shown in the figure Take (z=3m), and losses due to nozzle as (0.1

z ).

Sol.

E.E. 0-E

0+0+23 =0+

+3 +

+0.02

0

0

+10

+ 0.1

------- 1

C.E.:

(0.15)

2 v =

(0.075)

2 vE

Thus; vE=4 v ----2

1 & 2 gives;

= 0.554 and

=16

z

E.E. O-A

23= (

+

+z) A + 0.5

Thus; H.G.L. A = (

+z) A =23-1.5

=23 -1.5 *0.554 H.G.L. A=22.17m

E.G.L. A = (

+z+

) A =23-0.5

=23 -0.5 *0.554 E.G.L. A=22.72m

E.E.O-B

23= (

+

+z) B + 0.5

+0.02

0

=

Page 164: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 164

Thus; H.G.L.B = 23-(1.5 +0.02

0 )

H.G.L.B=20.4 m

E.G.L. B =H.G.L. B+

= 20.4 +0.55 E.G.L. B=20.95 m

Across the valve, the H.G.L. drops by (10

), or (5.54m). Hence at (c);

H.G.L.C=H.G.L.B-5.54 H.G.L.C=14.86m

E.G.L.C=E.G.L.B-5.54 E.G.L.C=15.41m

E.E.O-D

23= (

+

+z) D +(10.5+0.02

0

0 )

Thus; H.G.L.D=23-19.5*0.554 H.G.L.D=12.2m

E.G.L.D=H.G.L.D+

E.G.L.D=12.75m

At point E

H.G.L.E=

+ZE =0+3 H.G.L.E=3m

E.G.L.E=

+

+ ZE =0+16

+3 E.G.L.E=11.86m

Example:(7.2): in the figure shown;

Ki=0.5, L1=300m, D1 =600mm, 1=2mm, L2 =240m, D2=1m, 2=0.3mm, v=3*10-6

and

H=6m.

Determine the discharge through the system.

Sol.:

Applying E.E. from A to B, using

C.E(v2=v1(

)

2=v1*0.6

2);

6=

[0.5 +f1

00

0 +(1-0.6

2)

2 +f2

0

0.6

4 +0.6

4]

Thus;

6=

(1.0392+500f1+31.104f2) ……………….. 1

Page 165: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 165

For (

=0.0033) and (

=0.0003) and the Moody diagram, values of (f) are assumed for

the fully turbulent range;

i.e.; f1=0.026 & f2= 0.015

Thus; from equ. 1 we obtain; v1=2.848 m/s

and v2= 1.025 m/s

Re1=

=

0

0 Re1=569600

Re2=

=

0

0 Re2=341667

Again, from moody diagram, with these (Re1, Re2) and (

,

) we obtain;

f1=0.0265 and f2= 0.0168

From equ. 1 , we obtain v1=2.819 m/s

Thus, Q=A1V1=

D1

2v1 Q=0.797 m

3/s

Ex: (7.3) In the figure shown, L1=900m, D1=300mm, 1=0.3 mm, L2=600m,

D2=200mm, 2=0.03mm, L3=1200m, D3=400mm, 3=0.24mm, =1028kg/m3, v=2.8*10

-

6m

2/s, pA=560kpa, ZA=30m, ZB=24m.

For a total flow of (340 L/s), determine the flow

through each pipe and the pressure at (B).

Sol.

Assume Q'1 =85 L/s =

=1.2 m/s

Re'1=

=129000

=0.001 Moody Diagram

=0.022

hf'1=

=0.022

00

0

× h

=4.85m

For Pipe 2

h

= h =4.85m =

assuming f'2=0.02 (fully turbulent,

=0.00015), thus.

=1.26 m/s,

Page 166: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 166

Re'2=

=91400, from Moody Diagram,

=0.019 and =1.291 m/s

Q'2=

D'2 2 Q'2=40.6 L/s

For Pipe 3

hf'3= hf'1 =4.85m = f'3 00

0

with (

=0.0006) assume f'3=0.02, then V'3=1.259 m/s, Re'3=180000, and hence;

f'3=0.02 Q'3=158.2 L/s

The total discharge Q'=Ʃ Q'= Q'1+ Q'2+ Q'3 Q'=283.8 L/s

Hence; Q1=

; Q2=

; Q3=

Thus; Q1= 101.3 L/s Q2 =48.64 L/s Q3 =189.53 L/s

The values of (hf):

v1=

=1.436 m/s Re1=155000 f1=0.021 hf1 =6.62 m

v2=1.548 m/s Re2=109500 f2=0.019 hf2 =6.62m

V3=1.512 m/s Re3=216000 f3=0.019 hf3 =6.64m

Thus, (hf1= hf2= hf3 ) and the solution is over. To find (pB);

E.E.A-B

+ ZA =

+ ZB +hf

=

0000

0 +30 -24 -6.64 = 54.8

Hence PB =54.8*1028*9.8 PB =552.5 kPa

Examle (7.4): In the figure shown; find the dis charges for water at (20˚ c) with the

following pipes data and reservoir elevations:

L1=3000 m D1=1m

=0.0002

L2 = 600m D1= 0.45m

= 0.002

L3 = 1000m D3 =0.6 m

=0.001

Z1=30m Z2=18m Z3=9m

Sol.:

Assume (

+Z)J =23 m

Page 167: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 167

E.E. 1-J 30=23+hf1 hf1 =7=f1

000

f1=0.014 V1=1.75 m/s

Q1=1.38m3/s

E.E. J-2 5=f2 00

0

f2=0.024 V2=1.75 m/s Q2=0.278m

3/s

E.E. J-3 14=f3 000

0

f3=0.02 V3=2.87 m/s Q3=0.811m

3/s

So that; (Inflow =Q1=1.38 m3/s) is greater than the out flow (Q2+ Q3= 0.278 + 0.811=

1.089) by amount (0.291m3/s).

Assume ((

+Z)J =24.6 m; and similarly);

E.E. 1-J 5.4= f1 000

f1=0.015 V1=1.534 m/s Q2=1.205m

3/s

E.E. J-2 6.6= f2 00

0

f2=0.024 V2=2.011 m/s Q2=0.32m

3/s

E.E. J-3 15.6= f3 000

0

f3=0.02 V3=3.029 m/s Q3=0.856m

3/s

Inflow is still greater by (0.029 m3/s). By extrapolating linearly,

(

+Z)J=24.8m Q1=1.183m

3/s Q2=0.325m

3/s Q3=0.856m

3/s

Example (7.5): Calculate the discharge through each pipe of the network shown in the

figure. Take (n=2).

Sol.:

First Trail

Loop 1 Loop 2

r Q0n n rQ0

n-1 r Q0

n n rQ0

n-1

1*602=3600 2*1*60=120

3*52=75 2*3*5=30

2*402=-3200 2*2*40=160

Ʃ r Q0n=475 Ʃǀn rQ0

n-1 ǀ=310

∆Q= -

0 ≈ -1.5

2*302 =1800 2*2*30=120

3*52=-75 2*3*5=30

1*452=-2025 2*1*45=90

ƩrQ0n =-300 Ʃ n rQ0

n-1ǀ=240

∆Q= - 00

0 ≈ 1

Page 168: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 168

Trial 2 Q=Q0+∆Q

2.5=5+(-1.5)-1

Thus ∆Q≈0 for all loops, and hence the final distribution will be;

Example (7.6): A pump characteristics are given

by; (hp =31.12000Q2) and (ƺp =-190000Q

2+8590Q),

where (hp) is in (m) and (Q) in (m3/s) and (ƺp) is the

efficiency (%).

a. Find the characteristics of three identical pumps

connected in parallel

b. For the piping system shown in the figure,

estimate the difference in operational cost between one pump and three pumps in

parallel to supply (1000m3) of water to the upper reservoir if the cost of (1KWh) is

(65 fils). Neglect minor losses

c. Repeat (a) and (b) for three identical pumps in series.

Sol.:

(a) Qe=3Q1=3Q2=3Q3=3Q

hpe=hp1=hp2=hp3 hpe=31-12000 (

)2

ƺpe = ƺp1= ƺp2= ƺp3 ƺpe=-190000(

)2

+8590(

)

Loop 1 Loop2

r Q0n n rQ0

n-1 r Q0

n n rQ0

n-1

1*58.52=3422.25 117

3*2.52=18.75 15

2*41.52=-3444.5 166

Ʃ r Q0n =-3.5 Ʃǀn rQ0

n-1 ǀ=298

∆Q= -

=0.012

2*312=1922 124

3*2.52=-19 15

1*442=-1936 88

Ʃ r Q0n =-33 Ʃǀ n rQ0

n-1 ǀ=227

∆Q= -

=0.145

Page 169: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 169

(b) E.E hp =15+hf=15+f

Or ; hp =15+65352Q2------- (1)

One pump

31-12000Q2=15+65352Q

2

Q=0.01438m

3/s

hp=31-12000(0.01438)2 hp=28.51m

p =-190000(0.01438)2+8590(0.01438) p=84.23%

Ip=

Ip=4774.5W

t =

=

000

0 0 t=695410.3 s

no. of KWh= Ip*t=

000 * 0

00 no. of KWh=922.3

cost. =922.3*0.065 cost =59.95 ID

Three Pumps

Qe=3Q1=3*0.01438 Qe=0.04314m3/s

hpe =hp1=hp2=hp3 hpe =28.51m

pe = p1 = p2= p3 pe =84.23%

t=

=

000

0 0 t=231803.4 s

Ip=

Ip=14324.5 W

no.of KWh= Ip*t no. of KWh=922.3

cost. =922.3*0.065 cost =59.95 ID

Thus, there is no difference in cost. Only the time will be reduced

(c) Qe=Q1=Q2=Q3=Q

hpe=3Q1=3Q2=3Q3 hpe=93-36000 Q2

ƺpe = ƺp1= ƺp2= ƺp3 ƺpe=-190000Q2+8590

One pump; the same as in (b)

Three Pumps in Series

Qe=Q1=Q2=Q3=Q Qe=0.01438 m3/s

hpe =3 hp =3*28.51 hpe =85.53

ƺpe = ƺp1= ƺp2= ƺp3 ƺpe=84.23%

Page 170: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 170

Ip=

Ip=14324.5 W

t=

=

000

0 0 t=695410.3 s

no. of KWh= Ip*t no. of KWh=2767

Cost. =2767*0.065 cost. =179.86 ID

Cost is higher than for single pump.

Example(7.7): Determine the head loss, in millimeters of water, required for flow of

(300 m3/min) of air at (20˚c) and (100 kpa) through a rectangular galvanized-iron section

(700 mm) wide, (350mm) high, and (70m) long.

Sol.:

Rh=

=

0 0

(0 0 ) Rh=0.117 m

Dh=2 Rh Dh=0.468m

=

=

0 000

0

= 0.00032

V=

=

00 0

0 0 v=20.41 m/s

=

=

00000

=1.189 kg/m

3

From Fig. (c.1); =2.2*10-5

Pa. s

Re=

=

0 0

0 Re=516200

From Moody Diagram; f=0.0165

Thus;

hf= f

= 0.0165 0

0 0

hf=52.42 m air

ɣ air = air g =1.189*9.8 ɣ air =11.66 N/m3

Thus;

hf (mH2O)= hf *

= 52.42 *

0 O O

Page 171: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 171

Problems

The problems number listed in the table below refer to the problems in the

"text book", chapter (10)

Article No. Related Problems

7.3 1,2,3,5,6,7,8

7.4 10,11,15,17,19,28,31,32,38,40,41

7.5 20,22,23,24,25,26,27,33,34,35,36,37,39

7.6 44, 45,46,47

Page 172: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 172

Appendix –A-

COURSE FOLIO

Course Title – Symbol: Fluid Mechanics / I – ME202

Instructor:

Prof. Dr. Ihsan Y. Hussain

Professor of Mechanical Engineering / Thermo-Fluids

Mech. Engr. Dept.

College of Engineering

University of Baghdad

Tel: +00964-7901781035

Email: [email protected] ; [email protected] :

[email protected]

Teaching Assistant:

Dr. Ammar A. Farhan

Lecturer of Mechanical Engineering / Thermo-Fluids

Mech. Engr. Dept.

College of Engineering

University of Baghdad

Tel: +00964-7903566684

Email: [email protected]

Course Description (or Catalog Data)

ME202 - Fluid Mechanics / I

This course introduces the description of phenomena associated with fluid flow.

Topics covered: physical properties of fluids; fluid statics; principles of conservation of

mass, energy and momentum; control volume technique; Bernoulli equation; dimensional

analysis and similitude; viscous flow in pipes and channels; laminar and turbulent flow;

Page 173: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 173

boundary layer theory; drag and lift; Moody diagram; pipe problems; flow and fluid

measurements; analysis of pipes and pumps networks. Physical understanding of fluid

flows and applications to practical problems will be stressed. The course is designed to

provide a background to higher level courses involving fluid flow and heat transfer. The

course is taught through 5 hrs per week, 3 theories, 1 tutorial, and 1 experimental.

Prerequisites: ME101 & ME102 Courses

Goals / Objectives

1. Introduce basic definitions and introductory concepts of fluid mechanics.

2. Introduce the description of pressure distribution in a static fluid and its effects on

submerged surfaces and bodies.

3. Introduce the description of phenomena associated with fluid flow phenomena.

4. Explain and derive the conservation laws that govern fluid motion ( continuity,

energy, and momentum equations).

5. Introduce the principles of “Dimensional Analysis” and “Similitude” and their

application to fluid mechanics problems.

6. Introduce the principles of viscous flow, boundary layer, drag and lift, primary and

secondary losses in pipe flow.

7. Enable the student to analyze and design pipes network and pumps connection.

8. Enable the student to measure the fluid properties and flow parameters, and to

design and conduct experiments of fluid mechanics.

9. Provide a strong physical and analytical understanding of fluid

flows in order to function in the capacity of mechanical engineer in

an engineering company dealing with fluid machinery.

10. Provide a background to higher level courses involving fluid flow

and head transfer.

Student Learning Outcomes

At the end of the class, the student will be able to:

Page 174: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 174

a. Define Fluids and Fluid Mechanics and distinguish between

incompressible and compressible fluids, and understand and define

the basic fluid properties; especially density and viscosity, and

apply Newton’s law of viscosity.

b. Calculate; the pressure in static fluid, hydrostatic forces on

submerged surfaces, buoyancy forces, stability of submerged and

floating bodies, Metacenter, and forces on accelerated fluids.

c. Be familiar with continuity, energy, and momentum equations, and

their applications to fluid flow problems.

d. Understand and apply the principles of dimensional analysis and

similitude to fluid mechanics problems.

e. Formulate and solve incompressible laminar flows for simple

parallel flows in Cartesian and polar coordinates.

f. Analyze boundary layer flows over flat plate.

g. Estimate drag and lift forces in laminar and turbulent flows for

different immersed bodies.

h. Calculate frictional losses in pipe problems for both laminar and

turbulent flows, by using Moody Diagram.

i. Calculate secondary ( minor ) losses for various pipes fittings and

connections.

j. Know how to measure flow properties ( pressure, velocity,

discharge ) and fluid properties ( density and viscosity ).

k. Be able to analyze and design pipes network and connection, and

pumping stations and connection.

l. Be able to apply modern knowledge and to apply mathematics,

science, engineering and technology to fluid mechanics problems

and applications.

m. Design and conduct experiments of fluid mechanics, as well as

analyze, interpret data and apply the experimental results for the

services.

Page 175: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 175

n. Work in groups and function on multi-disciplinary teams.

o. Identify, formulate and solve engineering fluid mechanics

problems.

p. Understand professional, social and ethical responsibilities.

q. Communicate effectively.

r. Use the techniques, skills, and modern engineering tools necessary

for engineering practice in fluid mechanics applications.

Course Schedule

Hours / Week Theoretical Content Week

Exp. Tut. Theo.

1 1 3 Introductory Concepts To Fluid

Mechanics 1

1 1 3 Introductory Concepts To Fluid

Mechanics 2

1 1 3 Fluid Statics : Pressure Distribution In

Static Fluids 3

1 1 3 Pressure Measurements 4

1 1 3 Forces On Immersed Surfaces 5

1 1 3 Forces On Immersed Surfaces 6

1 1 3 Buoyancy And Floatation 7

1 1 3 Buoyancy And Floatation 8

1 1 3 Buoyancy And Floatation 9

1 1 3 Accelerated Fluid And Relative

Motion 01

1 1 3 Introduction To Fluid Motion 00

1 1 3 Continuity Equation 02

1 1 3 Energy Equation 03

1 1 3 Momentum Equation 04

1 1 3 Momentum Equation 05

1 1 3 Dimensional Analysis And Similitude 06

Page 176: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 176

1 1 3 Dimensional Analysis And Similitude 07

1 1 3 Dimensional Analysis And Similitude 08

1 1 3 Laminar Viscous Flow Between Parallel

Plates 09

1 1 3 Laminar Viscous Flow Through Circular

Tubes 21

1 1 3 Boundary Layer Theory, Drag & Lift 20

1 1 3 Losses In Pipes : Moody Diagram 22

1 1 3 Losses In Pipes : Moody Diagram 23

1 1 3 Losses In Pipes : Moody Diagram 24

1 1 3 Measurements Of Fluid Flow 25

1 1 3 Measurements Of Fluid Flow 26

1 1 3 Measurements Of Fluid Flow 27

1 1 3 Analysis Of Piping And Pumping

Networks 28

1 1 3 Analysis Of Piping And Pumping

Networks 29

1 1 3 Analysis Of Piping And Pumping

Networks 31

Textbook and References

1. “Fluid Mechanics”; by Victor L. Streeter and E. Benjamin Wylie,

First SI Metric Edition, M G. GNW Hill , 1988.

2. “Fundamental of Fluid Mechanics”; by Bruce E. Munson,

Theodore H. Okiishi, and Wade W. Huesch, Benjamin

Wylie, Sixth Edition, 2009

3. “Fluid Mechanics : Fundamentals and Applications”; by

Yunus A. Çengel and John M. Cimbala, M G. GNW Hill

Higher Education, 2006

4. “Introductory Fluid Mechanics” ; by Joseph Katz,

Cambridge University Press, 2010

Page 177: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 177

5. “Elementary Fluid Mechanics”, by John K. Vennard and

Robert L. Streat, 5th

ed., John Wiley and Sons, 1976.

6. “Engineering Fluid Mechanics by John A. Robert and

Clayton T. Crow, 2nd

ed., Houghton Mifflin Coo, 1988.

Grading Units

Annual Semester System Academic

System

Final

Examination

Laboratory

Work Quest

Course

Assessment for

Annual System

(011)%

70% \

30 % ( Tests, , Quizzes, and

Extracurricular Activities )

1- The laboratory experiments are included in the

general course (Laboratories / 2).

2- Two - Three tests are made; and not Less than (20-

25) Quizzes are usually made.

Additional

Information

Typical Grading

Excellent 90-100%

Very Good 80-89%

Good 70-79%

Fair 60-69%

Pass 50-59%

Poor <50%

Grading Policy

1. Q uizzes:

- There will be a ( 20 – 25 ) closed books and notes quizzes during

the academic year.

- The quizzes will count 20% of the total course grade.

2. Tests, 2-3 Nos. and will count 10% of the total course grade.

3. Extracurricular Activities, this is optional and will count extra marks

( 1 – 5 % ) for the student, depending on the type of activity.

4. Final Exam:

Page 178: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 178

- The final exam will be comprehensive, closed books and notes,

and will take place on

(Saturday-8th

) , ( January ), 2013 from 9:00 AM - 12:00 PM in

rooms ( M12 + M13 )

- The final exam will count 70% of the total course grade

Assessment Plan

1. Reinforcement is done through tests, quizzes, extracurricular

activities and student engagement during lectures as shown in the

table below.

Course Outcomes Strategies/Actions Assessment Methods

a) Define Fluids and Fluid

Mechanics and distinguish

between incompressible

and compressible fluids,

and understand and define

the basic fluid properties;

especially density and

viscosity, and apply

Newton’s law of viscosity.

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

b) Calculate; the pressure in

static fluid, hydrostatic

forces on submerged

surfaces, buoyancy

forces, stability of

submerged and floating

bodies, Metacenter, and

forces on accelerated

fluids.

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

c) Be familiar with

continuity, energy, and

momentum equations, and

their applications to fluid

flow problems.

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

d) Understand and apply

the principles of

Lecture plan and in-class

activities: each class will

In-class questions and

discussion

Page 179: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 179

dimensional analysis

and similitude to fluid

mechanics problems.

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

Quizzes

Lab. Experiments

e) Formulate and solve

incompressible laminar

flows for simple parallel

flows in Cartesian and

polar coordinates.

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

f) Analyze boundary layer

flows over flat plate.

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

g) Estimate drag and lift

forces in laminar and

turbulent flows for

different immersed

bodies.

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

h) Calculate frictional

losses in pipe problems

for both laminar and

turbulent flows, by

using Moody Diagram.

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

Page 180: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 180

i) Calculate secondary (

minor ) losses for

various pipes fittings

and connections .

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discusion

Quizzes

Lab. Experiments

j) Know how to measure

flow properties (

pressure, velocity,

discharge ) and fluid

properties ( density and

viscosity ).

Lecture plan and in-class

activities: each class will

commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

k) Be able to analyze and

design pipes network

and connection, and

pumping stations and

connection.

Lecture plan and in-class

activities: each class

will commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

l) Be able to apply modern

knowledge and to apply

mathematics, science,

engineering and

technology to fluid

mechanics problems and

applications.

Lectures

Experiments

Tests and Exams

Extracurricular

activities

In-class questions and

discussion

Quizzes

Lab. Experiments

Extracurricular

activities

m) Design and conduct

experiments of fluid

mechanics, as well as

analyze, interpret data

and apply the

experimental results for

the services.

Conducting

experiments in Fluid

Mechanics Lab. and

technical writing of

reports including

discussions and

conclusions

In-class questions and

discussion

Quizzes

Lab. Experiments

n) Work in groups and

function on multi-

disciplinary teams.

Conducting

experiments in

groups

Tutorial hour work

Extracurricular

Monitoring, Guiding,

Evaluation, Quizzes …..

Page 181: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 181

activities

o) Identify, formulate and

solve engineering fluid

mechanics problems.

Homework , Tutorial

hour, Solved Examples

…..

In-class questions and

discussion

Quizzes

Tests

p) Understand professional,

social and ethical

responsibilities.

In- and Out-Class oral

conservations,

lectures….

Discussions and

conservations

Extracurricular

activities

q) Communicate

effectively.

In- and Out-Class oral

conservations,

lectures….

Discussions and

conservations

Extracurricular

activities

r) Use the techniques,

skills, and modern

engineering tools

necessary for

engineering practice in

fluid mechanics

applications.

In- and Out-Class oral

conservations,

lectures….

Discussions and

conservations

Extracurricular

activities

s) Be able to analyze and

design pipes network

and connection, and

pumping stations and

connection.

Lecture plan and in-class

activities: each class

will commence with a

summary of the

previous lecture,

questions will be asked

and the responses will be

used to evaluate the

students’ understanding

of the topics covered.

In-class questions and

discussion

Quizzes

Lab. Experiments

t) Be able to apply modern

knowledge and to apply

mathematics, science,

engineering and

technology to fluid

mechanics problems and

applications.

Lectures

Experiments

Tests and Exams

Extracurricular

activities

In-class questions and

discussion

Quizzes

Lab. Experiments

Extracurricular

activities

u) Design and conduct

experiments of fluid

mechanics, as well as

analyze, interpret data

and apply the

experimental results for

the services.

Conducting

experiments in Fluid

Mechanics Lab. and

technical writing of

reports including

discussions and

conclusions

In-class questions and

discussion

Quizzes

Lab. Experiments

v) Work in groups and

function on multi-

disciplinary teams.

Conducting

experiments in

groups

Tutorial hour work

Monitoring, Guiding,

Evaluation, Quizzes …..

Page 182: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 182

Extracurricular

activities

w) Identify, formulate and

solve engineering fluid

mechanics problems.

Homework , Tutorial

hour, Solved Examples

…..

In-class questions and

discussion

Quizzes

Tests

x) Understand professional,

social and ethical

responsibilities.

In- and Out-Class oral

conservations,

lectures….

Discussions and

conservations

Extracurricular

activities

y) Communicate

effectively.

In- and Out-Class oral

conservations,

lectures….

Discussions and

conservations

Extracurricular

activities

z) Use the techniques,

skills, and modern

engineering tools

necessary for

engineering practice in

fluid mechanics

applications.

In- and Out-Class oral

conservations,

lectures….

Discussions and

conservations

Extracurricular

activities

2. Lists the responses obtained from student survey conducted at the end of

academic year. A student’s opinion questionnaire was made for a selected

specimen of the students. The results of this questionnaire are shown in

Table ( 1 ) and figure ( 1 ) for the students opinion about curriculum , and in

Table ( 2 ) and figure ( 2 ) for the students opinion about faculty member.

Page 183: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 183

Table ( 1 ): Students Opinion Questionnaire about Curriculum

Academic Year 2010 – 2011

Code No. & Curriculum Name: : ME 202 FLUID MECHANICS / I

Year: 2nd

Year

Faculty Member's Name: Prof. Dr. Ihsan Y. Hussain

Dear Students: For the development of the educational process at the university, we

hope to express your opinion by answering accurately with mark √ in the place

which reflects your opinion taking into consideration the accuracy and objectivity.

Score 1 2 3 4 5

No. Question Strongly

Agree Agree

I

Don’t

Know

Disagree

I Don’t

Agree At

All

1 Overall, this Curriculum subject is

good and useful 9 7 0 0 0

2 Lecture time is sufficient to cover

the contents of the article 7 6 0 3 0

3 The content of article commensurate

with the objective of Curriculum 6 9 1 0 0

4 Subject content is an interdependent

information 5 7 1 3 0

5 Textbooks and references are

available and meaningful 3 7 1 5 0

6 available of References helpful for

stimulate and thinking 2 8 2 1 3

7 The book is free of grammatical

errors Printing 3 6 5 2 0

8 Contents of the book are of outdated

information 2 6 7 0 1

9 The book contains a variety of

examples and exercises 7 7 1 1 0

10 The evaluation of the subject system

is appropriate (test method) 6 7 1 0 2

11 Exams reflect the content of the

subject 6 6 1 3 0

12 Number of exams be exhaustive of

the content subject 6 8 2 0 0

13 Examinations and assignments

helped to absorb the subject 5 8 0 0 3

14 Examinations and exercises are in

line with the objectives of the

subject

5 8 1 2 0

15 Examinations and exercises help to

think of more conservation 5 9 0 2 0

16 Number of exams and the their

recurrence are appropriate 6 6 2 1 1

17 The case of equipped lecture halls

satisfactory 2 3 0 5 6

18 Capabilities and laboratories are

appropriate and effective 1 1 6 8

Page 184: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 184

Table ( 2 ): Students Opinion Questionnaire about Faculty Member

Academic Year 2010 - 2011

Code No. & Curriculum Name: ME 202 - FLUID MECHANICS (1)

Year: 2nd

Year Faculty Member's Name: Dr. Ihsan Y. Hussain

Is the plan of teaching the subject was distributed from the beginning of the year? Yes

No I don’t know

Is the faculty member is committed to the specific office hours of the subject? Yes No

I don’t know

If the answer is (No) explained that___________

Dear Students: For the development of the educational process at the university we hope to

express your opinion by answering accurately with mark √ in the place which reflects your

opinion taking into consideration the accuracy and objectivity.

Score 1 2 3 4 5

No. Question Strongly

Agree Agree

I

Don’t

Know

Disagree

I Don’t

Agree At

All

1 Has the ability to communicate

scientific material in a smooth and

easy manner

2 11 1 1 1

2 Keep to use the tools and techniques

of modern education 1 2 2 9 2

3 Illustrates the theoretical aspects in

the subject with examples from the

reality

3 11 0 2 0

4 Gives the scientific material in a

manner covering the time of the

lecture

3 8 1 4 0

5 Committed to the dates of lectures 12 4 0 0 0

6 Improve in the management ranks

and give equal opportunities to

students in dialogue and discussion

1 12 1 1 1

7 Motivates students and encourages

them to think and research 0 10 1 4 1

8 Respects the different views of the

students 1 13 1 1 0

9 Through self-learning encourages

students to search for what is new

and modern

1 7 2 5 1

10 Accept criticism and suggestions

with an open mind 0 7 7 1 1

11 Be objective and fair in his / her

evaluation of students 2 10 3 1 0

12 Uses a variety of methods to assess

the performance of students (such as

reports, research, and quizzes),

4 4 1 7 1

13 Follow up activities and duties to

put the evaluation weights 0 2 5 9 0

14 Has the ability to discuss all issues

of the subject 10 4 1 0 1

15 Working to increase the knowledge

of the outcome requested 2 10 1 2 1

3

13

12 1

3

Page 185: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 185

Figure (1): Students Opinion Questionnaire about Fluid Mechanics (1)

Curriculum

Figure (2): Students Opinion Questionnaire about Fluid Mechanics (1)

Instructor

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

% o

f A

nsw

er

for

Each

Se

rie

s

Question No.

Students Opinion - Curricula

Series1 Series2 Series3 Series4 Series5

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

% o

f A

nsw

er

for

Each

Se

rie

s

Question No.

Students Opinion - Faculty Member

Series1 Series2 Series3 Series4 Series5

Page 186: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 186

3. Students rating performance: Table ( 3 ) shows the results of quizzes and tests related

to some of the course outcomes.

Table ( 3 ): Students Rating Related to some of the Course LOs

Mark ( 10 % )

Theoretical Content LO %

Success St. Dev. Avg.

48.8 % 4.7 Introductory Concepts To Fluid

Mechanics

a

58.5 % 5.1 Introductory Concepts To Fluid

Mechanics

33.3 % 3.95 Fluid Statics : Pressure Distribution In

Static Fluids & Pressure Measurements

b 31.1 % 3.8 Forces On Immersed Surfaces

13 % 2.1 Buoyancy And Floatation

17.5 % 3.1 Accelerated Fluid And Relative

Motion

84.4 % 6.7 Continuity Equation

c 29.8 % 3.05 Energy Equation

4 % 1 Momentum Equation

Dimensional Analysis And Similitude

d Dimensional Analysis And Similitude

Dimensional Analysis And Similitude

30.1 % 3.15 Test / I a, b,

c, d

68.9 % 5 Laminar Viscous Flow Between Parallel

Plates

e

40 % 3.9 Laminar Viscous Flow Through Circular

Tubes

52.9 % 5 Boundary Layer Theory f

58.5 % 5.35 Drag & Lift g

Losses In Pipes : Moody Diagram h &

i Losses In Pipes : Moody Diagram

Page 187: Incompressible Fluid Mechanics - University of Baghdad...Incompressible Fluid Mechanics 2017 Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Incompressible Fluid Mechanics 2017

Prof. Dr. Ihsan Y. Hussain / Mech. Engr. Dept. - College of Engr. – University of Baghdad

Page 187

Losses In Pipes : Moody Diagram

Measurements Of Fluid Flow

j Measurements Of Fluid Flow

Measurements Of Fluid Flow

Analysis Of Piping And Pumping

Networks

k Analysis Of Piping And Pumping

Networks

Analysis Of Piping And Pumping

Networks

Results of Tables 1, 2, and 3 are used in Table 4 to assess changes/improvements from

the previous evaluation as well as changes/improvements that will be made to the course

to improve student achievement of the learning outcomes.

Table ( 4 ): Changes/Improvements Term

Assessment of

changes/improvements

made in previous term

Good improvement in

experimental part

Good response from students

for the extracurricular

activities

Good response for the case of

the subject submitted to the

students, which includes

lectures and modern

references

Changes/improvements

that will be made next

time the subject is

offered

Use the tools and techniques of

modern education

Use of Interactive Class

Using scientific films and videos in teaching the subject

Increase the number of extracurricular activities

Decrease the number of quizzes

Improve Laboratory equipment